drm/i915: Fix error handling for cursor/sprite plane create failure

intel_cursor_plane_create() and intel_sprite_plane_create() return
an error pointer, so let's not mistakenly look for a NULL pointer.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reported-by: NChris Wilson <chris@chris-wilson.co.uk>
References: https://lists.freedesktop.org/archives/intel-gfx/2016-November/110690.html
Fixes: b079bd17 ("drm/i915: Bail if plane/crtc init fails")
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1478550057-24864-5-git-send-email-ville.syrjala@linux.intel.comReviewed-by: NChris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_display.c

@@ -15289,14 +15289,14 @@ static int intel_crtc_init(struct drm_i915_private *dev_priv, enum pipe pipe)
 		struct intel_plane *plane;
 
 		plane = intel_sprite_plane_create(dev_priv, pipe, sprite);
-		if (!plane) {
+		if (IS_ERR(plane)) {
 			ret = PTR_ERR(plane);
 			goto fail;
 		}
 	}
 
 	cursor = intel_cursor_plane_create(dev_priv, pipe);
-	if (!cursor) {
+	if (IS_ERR(cursor)) {
 		ret = PTR_ERR(cursor);
 		goto fail;
 	}