drm/fb-helper: Check fb_deferred_io_init() return value

The fb_deferred_io_init() can fail and return an errno code but currently
there is no check for its return value.

Fix that and propagate to errno to the caller in the case of a failure.

Fixes: d536540f ("drm/fb-helper: Add generic fbdev emulation .fb_probe function")
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230121192418.2814955-3-javierm@redhat.com

drivers/gpu/drm/drm_fbdev_generic.c

@@ -223,7 +223,9 @@ static int drm_fbdev_fb_probe(struct drm_fb_helper *fb_helper,
 		fbi->flags |= FBINFO_VIRTFB | FBINFO_READS_FAST;
 
 		fbi->fbdefio = &drm_fbdev_defio;
-		fb_deferred_io_init(fbi);
+		ret = fb_deferred_io_init(fbi);
+		if (ret)
+			return ret;
 	} else {
 		/* buffer is mapped for HW framebuffer */
 		ret = drm_client_buffer_vmap(fb_helper->buffer, &map);