drm/omap: dpi: Simplify clock setting API

The dpi_set_pll_clk() and dpi_set_dispc_clk() return various information
through pointer arguments that are never used by the callers. Remove
them to simplify the clock setting API.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Tested-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200226112514.12455-48-laurent.pinchart@ideasonboard.com