net: wwan: iosm: remove pointless null check

GCC 12 warns:

drivers/net/wwan/iosm/iosm_ipc_protocol_ops.c: In function ‘ipc_protocol_dl_td_process’:
drivers/net/wwan/iosm/iosm_ipc_protocol_ops.c:406:13: warning: the comparison will always evaluate as ‘true’ for the address of ‘cb’ will never be NULL [-Waddress]
  406 |         if (!IPC_CB(skb)) {
      |             ^

Indeed the check seems entirely pointless. Hopefully the other
validation checks will catch if the cb is bad, but it can't be
NULL.
Reviewed-by: M Chetan Kumar <m.chetan.kumar@intel.com>
Link: https://lore.kernel.org/r/20220519004342.2109832-1-kuba@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/wwan/iosm/iosm_ipc_protocol_ops.c

@@ -372,8 +372,6 @@ bool ipc_protocol_dl_td_prepare(struct iosm_protocol *ipc_protocol,
 struct sk_buff *ipc_protocol_dl_td_process(struct iosm_protocol *ipc_protocol,
 					   struct ipc_pipe *pipe)
 {
-	u32 tail =
-		le32_to_cpu(ipc_protocol->p_ap_shm->tail_array[pipe->pipe_nr]);
 	struct ipc_protocol_td *p_td;
 	struct sk_buff *skb;
 
@@ -403,14 +401,6 @@ struct sk_buff *ipc_protocol_dl_td_process(struct iosm_protocol *ipc_protocol,
 		goto ret;
 	}
 
-	if (!IPC_CB(skb)) {
-		dev_err(ipc_protocol->dev, "pipe# %d, tail: %d skb_cb is NULL",
-			pipe->pipe_nr, tail);
-		ipc_pcie_kfree_skb(ipc_protocol->pcie, skb);
-		skb = NULL;
-		goto ret;
-	}
-
 	if (p_td->buffer.address != IPC_CB(skb)->mapping) {
 		dev_err(ipc_protocol->dev, "invalid buf=%llx or skb=%p",
 			(unsigned long long)p_td->buffer.address, skb->data);