OMAPDSS: remove unneeded dss_ovl_wait_for_go()

There's an unnecessary wrapper function, dss_ovl_wait_for_go(), which
does nothing else than call dss_mgr_wait_for_go_ovl(). The
dss_ovl_wait_for_go() function can be removed.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>