usbvision-video: fix memory leak of alt_max_pkt_size

commit 090c65b694c362adb19ec9c27de216a808ee443c upstream.

1. usbvision->alt_max_pkt_size is not deallocated anywhere.
2. if allocation of usbvision->alt_max_pkt_size fails,
there is no proper deallocation of already acquired resources.
The patch adds kfree(usbvision->alt_max_pkt_size) to
usbvision_release() as soon as other deallocations happen there.
It calls usbvision_release() if allocation of
usbvision->alt_max_pkt_size fails as soon as usbvision_release()
is safe to work with incompletely initialized usbvision structure.
Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>