media: iris: use fallback size when S_FMT is called without width/height

media: iris: use fallback size when S_FMT is called without width/height

According to 4.5.1.5 of the M2M stateful decoder UAPI documentation,
providing the width and the height to S_FMT is "required only if it
cannot be parsed from the stream", otherwise they can be left as 0
and the S_FMT implementation is expected to return a valid placeholder
resolution that would let REQBUFS succeed.

iris was missing the fallback, so clients like rpi-ffmpeg wouldn't work.
Fix by adding an explicit fallback to defaults.

Fixes: b530b95de22c ("media: iris: implement s_fmt, g_fmt and try_fmt ioctls")
Link: https://github.com/jc-kynesim/rpi-ffmpeg/issues/103
Reviewed-by: Dikshita Agarwal <dikshita.agarwal@oss.qualcomm.com>
Signed-off-by: Val Packett <val@packett.cool>
Cc: stable@vger.kernel.org
Signed-off-by: Bryan O'Donoghue <bod@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>