media: amphion: ensure the bitops don't cross boundaries

the supported_instance_count determine the instance index range,
it shouldn't exceed the bits number of instance_mask,
otherwise the bitops of instance_mask may cross boundaries

Fixes: 9f599f35 ("media: amphion: add vpu core driver")
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Ming Qian <ming.qian@nxp.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>