staging/bcm2835-codec: Change the default codec res to 32x32

In order to effectively guarantee that a V4L2_EVENT_SOURCE_CHANGE
event occurs, adopt a default resolution of 32x32 so that it
is incredibly unlikely to be decoding a stream of that resolution
and therefore failing to note a "change" requiring the event.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>