scsi: lpfc: Fix lpfc overwrite of sg_cnt field in nvmefc_tgt_fcp_req

scsi: lpfc: Fix lpfc overwrite of sg_cnt field in nvmefc_tgt_fcp_req

In lpfc_nvmet_prep_fcp_wqe() the line "rsp->sg_cnt = 0" is modifying the
transport's data structure. This may result in the transport believing the
s/g list was already freed, thus may not unmap/free it properly.  Lpfc
driver should not modify the transport data structure.

The zeroing of the sg_cnt is to avoid use of the transport's sgl in a
subsequent loop where the driver builds the necessary requests for the
adapter firmware to complete the IO.

Change LLDD to use a local copy of the transport sg_cnt when building
requests to be passed to the adapter fw.

Link: https://lore.kernel.org/r/20200322181304.37655-4-jsmart2021@gmail.com
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>