drm/i915: Fix struct_mutex deadlock due to merge fumble

commit a8c6ecb3be7029881f7c95e5e201a629094a4e1a
Merge: 8dd0eb35 9eccca0
Author: Dave Airlie <airlied@redhat.com>
Date:   Mon Mar 9 19:58:30 2015 +1000

    Merge tag 'v4.0-rc3' into drm-next

managed to pick the wrong code to resolve the conflict and left us with
a mutex_lock(struct_mutex) without the mutex_unlock(struct_mutex) leading
to a deadlock. Fix the problem by recovering the correct code which doesn't
need the lock.

Cc: Dave Airlie <airlied@redhat.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/i915/intel_display.c

@@ -12295,9 +12295,7 @@ intel_check_cursor_plane(struct drm_plane *plane,
 		return -ENOMEM;
 	}
 
-	/* we only need to pin inside GTT if cursor is non-phy */
-	mutex_lock(&dev->struct_mutex);
-	if (!INTEL_INFO(dev)->cursor_needs_physical && obj->tiling_mode) {
+	if (fb->modifier[0] != DRM_FORMAT_MOD_NONE) {
 		DRM_DEBUG_KMS("cursor cannot be tiled\n");
 		ret = -EINVAL;
 	}