[media] v4l: compat: Prevent allocating excessive amounts of memory

get_v4l2_ext_controls32() is used to convert the 32-bit compat struct into
native 64-bit representation. The function multiplies the array length by
the entry length before validating size. Perform the size validation
first.

Also use unsigned values for size computation.

Make similar changes to get_v4l2_buffer32() for multi-plane buffers.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>