scsi: message: mptlan: Replace one-element array with flexible-array member

There is a regular need in the kernel to provide a way to declare having a
dynamically sized set of trailing elements in a structure. Kernel code
should always use "flexible array members"[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].

Refactor the code according to the use of a flexible-array member in struct
_SGE_TRANSACTION32 instead of one-element array.

Also, this helps with the ongoing efforts to enable -Warray-bounds by
fixing the following warning:

  CC [M]  drivers/message/fusion/mptlan.o
drivers/message/fusion/mptlan.c: In function ‘mpt_lan_sdu_send’:
drivers/message/fusion/mptlan.c:759:28: warning: array subscript 1 is above array bounds of ‘U32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds]
  759 |  pTrans->TransactionDetails[1] = cpu_to_le32((mac[2] << 24) |
      |  ~~~~~~~~~~~~~~~~~~~~~~~~~~^~~

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/109
Link: https://lore.kernel.org/r/20210324233344.GA99059@embeddedorSigned-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/message/fusion/lsi/mpi.h

@@ -424,8 +424,8 @@ typedef struct _SGE_TRANSACTION32
     U8                      ContextSize;
     U8                      DetailsLength;
     U8                      Flags;
-    U32                     TransactionContext[1];
-    U32                     TransactionDetails[1];
+    U32                     TransactionContext;
+    U32                     TransactionDetails[];
 } SGE_TRANSACTION32, MPI_POINTER PTR_SGE_TRANSACTION32,
   SGETransaction32_t, MPI_POINTER pSGETransaction32_t;
 

drivers/message/fusion/mptlan.c

@@ -72,9 +72,6 @@ MODULE_VERSION(my_VERSION);
 #define MPT_LAN_RECEIVE_POST_REQUEST_SIZE \
 	(sizeof(LANReceivePostRequest_t) - sizeof(SGE_MPI_UNION))
 
-#define MPT_LAN_TRANSACTION32_SIZE \
-	(sizeof(SGETransaction32_t) - sizeof(u32))
-
 /*
  *  Fusion MPT LAN private structures
  */
@@ -745,7 +742,7 @@ mpt_lan_sdu_send (struct sk_buff *skb, struct net_device *dev)
 	pTrans->ContextSize   = sizeof(u32);
 	pTrans->DetailsLength = 2 * sizeof(u32);
 	pTrans->Flags         = 0;
-	pTrans->TransactionContext[0] = cpu_to_le32(ctx);
+	pTrans->TransactionContext = cpu_to_le32(ctx);
 
 //	dioprintk((KERN_INFO MYNAM ": %s/%s: BC = %08x, skb = %p, buff = %p\n",
 //			IOC_AND_NETDEV_NAMES_s_s(dev),
@@ -1159,7 +1156,7 @@ mpt_lan_post_receive_buckets(struct mpt_lan_priv *priv)
 			__func__, buckets, curr));
 
 	max = (mpt_dev->req_sz - MPT_LAN_RECEIVE_POST_REQUEST_SIZE) /
-			(MPT_LAN_TRANSACTION32_SIZE + sizeof(SGESimple64_t));
+			(sizeof(SGETransaction32_t) + sizeof(SGESimple64_t));
 
 	while (buckets) {
 		mf = mpt_get_msg_frame(LanCtx, mpt_dev);
@@ -1234,7 +1231,7 @@ mpt_lan_post_receive_buckets(struct mpt_lan_priv *priv)
 			pTrans->ContextSize   = sizeof(u32);
 			pTrans->DetailsLength = 0;
 			pTrans->Flags         = 0;
-			pTrans->TransactionContext[0] = cpu_to_le32(ctx);
+			pTrans->TransactionContext = cpu_to_le32(ctx);
 
 			pSimple = (SGESimple64_t *) pTrans->TransactionDetails;