Use drm_gem_object_[handle_]unreference_unlocked where possible

Mostly obvious simplifications.

The i915 pread/pwrite ioctls, intel_overlay_put_image and
nouveau_gem_new were incorrectly using the locked versions
without locking: this is also fixed in this patch.

Signed-off-by: Luca Barbieri <luca@luca-barbieri.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/nouveau/nv04_crtc.c b/drivers/gpu/drm/nouveau/nv04_crtc.c
index d2f143e..a1d1ebb 100644
--- a/drivers/gpu/drm/nouveau/nv04_crtc.c
+++ b/drivers/gpu/drm/nouveau/nv04_crtc.c
@@ -926,9 +926,7 @@
 	nv_crtc->cursor.set_offset(nv_crtc, nv_crtc->cursor.offset);
 	nv_crtc->cursor.show(nv_crtc, true);
 out:
-	mutex_lock(&dev->struct_mutex);
-	drm_gem_object_unreference(gem);
-	mutex_unlock(&dev->struct_mutex);
+	drm_gem_object_unreference_unlocked(gem);
 	return ret;
 }