drm/nouveau: make cursor_set implementation consistent with other drivers

When xorg state tracker wants to hide the cursor it calls set_cursor
with NULL buffer_handle and size=0x0, but nouveau refuses to hide it
because size is not 64x64... which is a bit odd. Both radeon and intel
check buffer_handle before validating size of cursor, so make nouveau
implementation consistent with them.
Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nv04_crtc.c

@@ -943,14 +943,14 @@ nv04_crtc_cursor_set(struct drm_crtc *crtc, struct drm_file *file_priv,
 	struct drm_gem_object *gem;
 	int ret = 0;
 
-	if (width != 64 || height != 64)
-		return -EINVAL;
-
 	if (!buffer_handle) {
 		nv_crtc->cursor.hide(nv_crtc, true);
 		return 0;
 	}
 
+	if (width != 64 || height != 64)
+		return -EINVAL;
+
 	gem = drm_gem_object_lookup(dev, file_priv, buffer_handle);
 	if (!gem)
 		return -ENOENT;

drivers/gpu/drm/nouveau/nv50_crtc.c

@@ -349,14 +349,14 @@ nv50_crtc_cursor_set(struct drm_crtc *crtc, struct drm_file *file_priv,
 	struct drm_gem_object *gem;
 	int ret = 0, i;
 
-	if (width != 64 || height != 64)
-		return -EINVAL;
-
 	if (!buffer_handle) {
 		nv_crtc->cursor.hide(nv_crtc, true);
 		return 0;
 	}
 
+	if (width != 64 || height != 64)
+		return -EINVAL;
+
 	gem = drm_gem_object_lookup(dev, file_priv, buffer_handle);
 	if (!gem)
 		return -ENOENT;