OMAPDSS: remove struct dss_clock_info

Remove struct dss_clock_info, as it is not usable in a case where DSS
fclk comes from a dedicated PLL. Instead, just use the fclk rate in
place of dss_clock_info, as that is all that's needed.

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