ALSA: usb-audio: Kill timer properly at removal

The USB-audio MIDI code initializes the timer, but in a rare case, the
driver might be freed without the disconnect call.  This leaves the
timer in an active state while the assigned object is released via
snd_usbmidi_free(), which ends up with a kernel warning when the debug
configuration is enabled, as spotted by fuzzer.

For avoiding the problem, put timer_shutdown_sync() at
snd_usbmidi_free(), so that the timer can be killed properly.
While we're at it, replace the existing timer_delete_sync() at the
disconnect callback with timer_shutdown_sync(), too.

Reported-by:  <syzbot+d8f72178ab6783a7daea@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/681c70d7.050a0220.a19a9.00c6.GAE@google.com
Cc: <stable@vger.kernel.org>
Link: https://patch.msgid.link/20250519212031.14436-1-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>