target: Fix possible TFO->write_pending() sense_reason_t silent WRITE corruption

This patch fixes a possible case in transport_generic_new_cmd() where a
failure from TFO->write_pending() from a fabric module return something
other than -EAGAIN or -ENOMEM would cause a failed WRITE to silently
succeed.

Go ahead and return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE for this
special case instead of only just making noise with WARN_ON().

(v2: Fix incorrect exception return for all cases)

Cc: Christoph Hellwig <hch@lst.de>
Cc: Roland Dreier <roland@purestorage.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_transport.c

@@ -2127,7 +2127,7 @@ transport_generic_new_cmd(struct se_cmd *cmd)
 	/* fabric drivers should only return -EAGAIN or -ENOMEM as error */
 	WARN_ON(ret);
 
-	return 0;
+	return (!ret) ? 0 : TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
 
 queue_full:
 	pr_debug("Handling write_pending QUEUE__FULL: se_cmd: %p\n", cmd);