drm/i915: Make disable_cursor_plane similar to commit_cursor_plane.

Update cursor_addr when disable_plane is called.
This is required to make commit_cursor_plane take a
crtc_state and a plane_state.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1452164052-21752-5-git-send-email-maarten.lankhorst@linux.intel.com


Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>