OMAPDSS: DSI: remove clkin from dsi_clock_info

struct dsi_clock_info contains clkin field, which is the rate of the
PLL's input clock. This field is not needed, as it can be easily
retrieved by using the clk_get_rate().

This patch removes the clkin field.

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