Revert "lpfc: Delete unnecessary checks before the function call mempool_destroy"

This reverts commit 9be32181 which
caused a regression on hardware using the SLI3 interface.

Reported-by: Dick Kennedy <dick.kennedy@broadcom.com>
Cc: <stable@vger.kernel.org> # 4.6+
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: James Bottomley <jejb@linux.vnet.ibm.com>