ALSA: bcd2000: Fix a UAF bug on the error path of probing

When the driver fails in snd_card_register() at probe time, it will free
the 'bcd2k->midi_out_urb' before killing it, which may cause a UAF bug.

The following log can reveal it:

[   50.727020] BUG: KASAN: use-after-free in bcd2000_input_complete+0x1f1/0x2e0 [snd_bcd2000]
[   50.727623] Read of size 8 at addr ffff88810fab0e88 by task swapper/4/0
[   50.729530] Call Trace:
[   50.732899]  bcd2000_input_complete+0x1f1/0x2e0 [snd_bcd2000]

Fix this by adding usb_kill_urb() before usb_free_urb().

Fixes: b47a2229

 ("ALSA: MIDI driver for Behringer BCD2000 USB device")
Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20220715010515.2087925-1-zheyuma97@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>