scsi: qla4xxx: fix a potential NULL pointer dereference

[ Upstream commit fba1bdd2a9a93f3e2181ec1936a3c2f6b37e7ed6 ]

In case iscsi_lookup_endpoint fails, the fix returns -EINVAL to avoid NULL
pointer dereference.

Signed-off-by: Kangjie Lu <kjlu@umn.edu>
Acked-by: Manish Rangankar <mrangankar@marvell.com>
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin (Microsoft) <sashal@kernel.org>