media: ttusb-dec: avoid release of non-acquired mutex

ttusb_dec_send_command() invokes mutex_lock_interruptible() that can
fail but then it releases the non-acquired mutex. The patch fixes that.

Found by Linux Driver Verification project (linuxtesting.org).

Fixes: dba328ba

 ("media: ttusb-dec: cleanup an error handling logic")
Signed-off-by: Evgeny Novikov <novikov@ispras.ru>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>