[SCSI] lpfc: Adjust lpfc_scsi_buf allocation

Adjust lpfc_scsi_buf allocation to account for lun_queue_depth and
error handling

Under high load and high duress, the error handler could steal some
command resources from the normal i/o path. Rework to allocate
additional resources to avoid this scneario.

Signed-off-by: James Smart <James.Smart@emulex.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>