drm/i915: Remove some visibility checks from intel_crtc_update_cursor.

This is duplicated with intel_check_cursor_plane, and with all
non-atomic paths removed this should be dead code.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1452164052-21752-4-git-send-email-maarten.lankhorst@linux.intel.com


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