drm/pl111: Use simple_display_pipe prepare_fb helper

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Eric Anholt <eric@anholt.net>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20180405154449.23038-5-daniel.vetter@ffwll.ch

drivers/gpu/drm/pl111/pl111_display.c

@@ -377,19 +377,13 @@ static void pl111_display_disable_vblank(struct drm_simple_display_pipe *pipe)
 	writel(0, priv->regs + priv->ienb);
 }
 
-static int pl111_display_prepare_fb(struct drm_simple_display_pipe *pipe,
-				    struct drm_plane_state *plane_state)
-{
-	return drm_gem_fb_prepare_fb(&pipe->plane, plane_state);
-}
-
 static struct drm_simple_display_pipe_funcs pl111_display_funcs = {
 	.mode_valid = pl111_mode_valid,
 	.check = pl111_display_check,
 	.enable = pl111_display_enable,
 	.disable = pl111_display_disable,
 	.update = pl111_display_update,
-	.prepare_fb = pl111_display_prepare_fb,
+	.prepare_fb = drm_gem_fb_simple_display_pipe_prepare_fb,
 };
 
 static int pl111_clk_div_choose_div(struct clk_hw *hw, unsigned long rate,