drm: adp: Fix NULL vs IS_ERR() check in adp_plane_new()

The __drmm_universal_plane_alloc() function doesn't return NULL, it
returns error pointers.  Update the check to match.

Fixes: 332122e ("drm: adp: Add Apple Display Pipe driver")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>

Author: Dan Carpenter

drivers/gpu/drm/adp/adp_drv.c

@@ -233,9 +233,9 @@ static struct drm_plane *adp_plane_new(struct adp_drv_private *adp)
 					     ALL_CRTCS, &adp_plane_funcs,
 					     plane_formats, ARRAY_SIZE(plane_formats),
 					     NULL, DRM_PLANE_TYPE_PRIMARY, "plane");
-	if (!plane) {
+	if (IS_ERR(plane)) {
 		drm_err(drm, "failed to allocate plane");
-		return ERR_PTR(-ENOMEM);
+		return plane;
 	}
 
 	drm_plane_helper_add(plane, &adp_plane_helper_funcs);