net: ipa: use data space for command opcodes

The 64-bit data field in a transaction is not used for commands.
And the opcode array is *only* used for commands.  They're
(currently) the same size; save a little space in the transaction
structure by enclosing the two fields in a union.
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ipa/gsi_trans.h

@@ -60,8 +60,10 @@ struct gsi_trans {
 	u8 used;			/* # entries used in sgl[] */
 	u32 len;			/* total # bytes across sgl[] */
 
-	void *data;
-	u8 cmd_opcode[IPA_COMMAND_TRANS_TRE_MAX];
+	union {
+		void *data;
+		u8 cmd_opcode[IPA_COMMAND_TRANS_TRE_MAX];
+	};
 	struct scatterlist *sgl;
 	enum dma_data_direction direction;