media: vicodec: fix memchr() kernel oops

commit cb3b2ffb757e75fef40fb94bc093cbbf49a6bf6e upstream.

The size passed to memchr is too large as it assumes the search
starts at the start of the buffer, but it can start at an offset.

Cc: <stable@vger.kernel.org>      # for v4.19 and up
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>