drm/ili9225: Call MIPI DBI mode_valid helper

MIPI DBI drivers validate each mode against their native resolution.
Add this test to ili9225.

Signed-off-by: Thomas Zimmermann <[e-mail]>
Reviewed-by: Noralf Trønnes <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/tiny/ili9225.c

···
 }
 
 static const struct drm_simple_display_pipe_funcs ili9225_pipe_funcs = {
+	.mode_valid	= mipi_dbi_pipe_mode_valid,
 	.enable		= ili9225_pipe_enable,
 	.disable	= ili9225_pipe_disable,
 	.update		= ili9225_pipe_update,