media: amphion: fix CHECKED_RETURN issues reported by coverity

calling "vpu_cmd_send/vpu_get_buffer_state/vpu_session_alloc_fs"
without checking return value

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>