ALSA: usb-audio: us144mkii: Fix null-deref in tascam_midi_in_urb_complete()

ALSA: usb-audio: us144mkii: Fix null-deref in tascam_midi_in_urb_complete()

The smatch tool reported a potential null pointer dereference in
tascam_midi_in_urb_complete(). The 'tascam' variable, derived from
'urb->context', was checked for nullity in one place, but dereferenced
without a check in several other places.

This patch fixes the issue by adding a null check at the beginning of
the function. If 'tascam' is null, the function now safely exits.
This prevents any potential crashes from null pointer dereferences.

It also fixes a latent bug where 'usb_put_urb()' could
be called twice for the same URB on submission failure, which would
lead to a use-after-free error.

Fixes: 67afec157fe6 ("ALSA: usb-audio: us144mkii: Add MIDI support and mixer controls")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202508192109.lcMrINK1-lkp@intel.com/
Signed-off-by: Šerif Rami <ramiserifpersia@gmail.com>
Link: https://patch.msgid.link/20250819185133.10464-1-ramiserifpersia@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>