Remove the dss_dss_clk from dss_core's opt-clocks. dss_dss_clk already
defined as the dss main_clk, and thus is not needed as an opt-clock.

Remove opt-clocks for dss_dispc, as dispc only uses the main_clk.
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: NPaul Walmsley <paul@pwsan.com>