While line6_probe() may kick off URB for a control MIDI endpoint, the
function doesn't clean up it properly at its error path.  This results
in a leftover URB action that is eventually triggered later and causes
an Oops like:
  general protection fault: 0000 [#1] PREEMPT SMP KASAN
  CPU: 1 PID: 0 Comm: swapper/1 Not tainted
  RIP: 0010:usb_fill_bulk_urb ./include/linux/usb.h:1619
  RIP: 0010:line6_start_listen+0x3fe/0x9e0 sound/usb/line6/driver.c:76
  Call Trace:
   <IRQ>
   line6_data_received+0x1f7/0x470 sound/usb/line6/driver.c:326
   __usb_hcd_giveback_urb+0x2e0/0x650 drivers/usb/core/hcd.c:1779
   usb_hcd_giveback_urb+0x337/0x420 drivers/usb/core/hcd.c:1845
   dummy_timer+0xba9/0x39f0 drivers/usb/gadget/udc/dummy_hcd.c:1965
   call_timer_fn+0x2a2/0x940 kernel/time/timer.c:1281
   ....

Since the whole clean-up procedure is done in line6_disconnect()
callback, we can simply call it in the error path instead of
open-coding the whole again.  It'll fix such an issue automagically.

The bug was spotted by syzkaller.

Fixes: eedd0e95

 ("ALSA: line6: Don't forget to call driver's destructor at error path")
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>