scsi: fcoe: drop frames in ELS LOGO error path

Drop the frames in the ELS LOGO error path instead of just returning an
error.

This fixes the following kmemleak report:
unreferenced object 0xffff880064cb1000 (size 424):
  comm "kworker/0:2", pid 24, jiffies 4294904293 (age 68.504s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<(____ptrval____)>] _fc_frame_alloc+0x2c/0x180 [libfc]
    [<(____ptrval____)>] fc_lport_enter_logo+0x106/0x360 [libfc]
    [<(____ptrval____)>] fc_fabric_logoff+0x8c/0xc0 [libfc]
    [<(____ptrval____)>] fcoe_if_destroy+0x79/0x3b0 [fcoe]
    [<(____ptrval____)>] fcoe_destroy_work+0xd2/0x170 [fcoe]
    [<(____ptrval____)>] process_one_work+0x7ff/0x1420
    [<(____ptrval____)>] worker_thread+0x87/0xef0
    [<(____ptrval____)>] kthread+0x2db/0x390
    [<(____ptrval____)>] ret_from_fork+0x35/0x40
    [<(____ptrval____)>] 0xffffffffffffffff

which can be triggered by issuing
echo eth0 > /sys/bus/fcoe/ctlr_destroy

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>