OMAPDSS: DISPC: add missing prototype

dispc_mgr_is_enabled() was missing a prototype in dss.h
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/video/omap2/dss/dss.h

@@ -414,6 +414,7 @@ void dispc_mgr_set_cpr_coef(enum omap_channel channel,
 		struct omap_dss_cpr_coefs *coefs);
 bool dispc_mgr_go_busy(enum omap_channel channel);
 void dispc_mgr_go(enum omap_channel channel);
+bool dispc_mgr_is_enabled(enum omap_channel channel);
 void dispc_mgr_enable(enum omap_channel channel, bool enable);
 bool dispc_mgr_is_channel_enabled(enum omap_channel channel);
 void dispc_mgr_set_io_pad_mode(enum dss_io_pad_mode mode);