drm/st7586: Call MIPI DBI mode_valid helper

MIPI DBI drivers validate each mode against their native resolution.
Add this test to st7586.
Signed-off-by: NThomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: NNoralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20221202125644.7917-4-tzimmermann@suse.de

drivers/gpu/drm/tiny/st7586.c

@@ -263,6 +263,7 @@ static const u32 st7586_formats[] = {
 };
 
 static const struct drm_simple_display_pipe_funcs st7586_pipe_funcs = {
+	.mode_valid	= mipi_dbi_pipe_mode_valid,
 	.enable		= st7586_pipe_enable,
 	.disable	= st7586_pipe_disable,
 	.update		= st7586_pipe_update,