scsi: fnic: Remove set but not used 'fr_len'

scsi: fnic: Remove set but not used 'fr_len'

This addresses the following gcc warning with "make W=1":

drivers/scsi/fnic/fnic_fcs.c: In function ‘fnic_fcoe_send_vlan_req’:
drivers/scsi/fnic/fnic_fcs.c:379:6: warning: variable ‘fr_len’ set but
not used [-Wunused-but-set-variable]
  379 |  int fr_len;
      |      ^~~~~~

Link: https://lore.kernel.org/r/20200831081126.3251288-4-yanaijie@huawei.com
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>