scsi: libfc: Remove set but not used variable 'disc'

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

drivers/scsi/libfc/fc_rport.c: In function 'fc_rport_recv_flogi_req':
drivers/scsi/libfc/fc_rport.c:866:18: warning:
 variable 'disc' set but not used [-Wunused-but-set-variable]

It no used any more after
commit baa6719f ("libfc: Update rport reference counting")

Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Reviewed-by: Johannes Thumshirn <jth@kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>