anv: Refactor anv_get_format_plane() - explicit unsupported

The same local variable, 'plane_format', was returned on success *and*
failure. Be more explicit in distinguishing the two cases: return
'plane_format' on success and return 'unsupported' on failure.

This simplifies the diff in upcoming patches for
VK_EXT_image_drm_format_modifier.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
1 file changed