drm/jpeg: add init value for num_jpeg_rings

Need init new num_jpeg_rings to 1 on jpeg.

Signed-off-by: James Zhu <James.Zhu@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Richard Liang <rliang1@amd.com>
Tested-by: Ying Li <ying.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>