scsi: snic: Remove unused 'xfer_len' variable

clang with W=1 reports:

drivers/scsi/snic/snic_scsi.c:490:6: error: variable
  'xfer_len' set but not used [-Werror,-Wunused-but-set-variable]
        u64 xfer_len = 0;
            ^
This variable is not used so remove it.

Signed-off-by: Tom Rix <trix@redhat.com>
Link: https://lore.kernel.org/r/20230328001647.1778448-1-trix@redhat.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>