V4L/DVB (12436): stk-webcam: read buffer overflow

It tested the value of stk_sizes[i].m before checking whether i was in range.

Cc: Hans Verkuil <hverkuil@xs4all.nl>
Cc: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>