drm/i915: Fix error handling for the NV12 fb dimensions check

Let's not leak obj->framebuffer_references when we decide that
the framebuffer domensions are not suitable for NV12.

Cc: stable@vger.kernel.org
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Vidya Srinivas <vidya.srinivas@intel.com>
Fixes: e44134f2 ("drm/i915: Add NV12 support to intel_framebuffer_init")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181029140031.11765-1-ville.syrjala@linux.intel.comReviewed-by: Matt Roper <matthew.d.roper@intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -14544,7 +14544,7 @@ static int intel_framebuffer_init(struct intel_framebuffer *intel_fb,
 	     fb->height < SKL_MIN_YUV_420_SRC_H ||
 	     (fb->width % 4) != 0 || (fb->height % 4) != 0)) {
 		DRM_DEBUG_KMS("src dimensions not correct for NV12\n");
-		return -EINVAL;
+		goto err;
 	}
 
 	for (i = 0; i < fb->format->num_planes; i++) {