scsi: lpfc: Slight fast-path performance optimizations

Slightly rework some error check code paths for better streamlining.

Added compiler unlikely hints to allow slightly better optimization of the
fast-path.

Removed a few pointer checks that were obviously already valid.

Link: https://lore.kernel.org/r/20191018211832.7917-9-jsmart2021@gmail.com
Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>