scsi: ibmvfc: don't check for failure from mempool_alloc()

mempool_alloc() cannot fail when passed GFP_NOIO or any other gfp
setting that is permitted to sleep.  So remove this pointless code.

Signed-off-by: NeilBrown <neilb@suse.com>
Acked-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>