drm/fb-helper: Call dirty helper after writing to fbdev

If fbdev uses a shadow framebuffer, call the damage handler. Otherwise
the update might not make it to the screen.

v2:
* mark virtual screen as dirty (Ville)

Signed-off-by: Thomas Zimmermann <[e-mail]>
Fixes: 222ec45f4c69 ("drm/fb_helper: Support framebuffers in I/O memory")
Acked-by: Maxime Ripard <[e-mail]>
Acked-by: Sam Ravnborg <[e-mail]>
Cc: Thomas Zimmermann <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: Sam Ravnborg <[e-mail]>
Cc: Maarten Lankhorst <[e-mail]>
Cc: Maxime Ripard <[e-mail]>
Cc: David Airlie <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: Gerd Hoffmann <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_fb_helper.c

···
 	if (ret > 0)
 		*ppos += ret;
 
+	if (ret > 0)
+		drm_fb_helper_dirty(info, 0, 0, info->var.xres_virtual, info->var.yres_virtual);
+
 	return ret ? ret : err;
 }