panfrost: Bail out early when doing a wallpaper blit

panfrost: Bail out early when doing a wallpaper blit

The wallpaper blit is a bit special in that the operation is targetting
the current FB, but the u_blitter logic creates a new surface for it
which makes util_framebuffer_state_equal() return false. In that case
we don't want a new FB descriptor to be emitted/attached, so let's just
copy the new state into ctx->pipe_framebuffer and exit the function.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>