scsi: qedf: Remove set but not used variable 'fr_len'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/scsi/qedf/qedf_fip.c: In function 'qedf_fcoe_send_vlan_req':
drivers/scsi/qedf/qedf_fip.c:22:6: warning:
 variable 'fr_len' set but not used [-Wunused-but-set-variable]

It's never used since introduction and can be removed.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Manish Rangankar <mrangankar@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>