omap2 clock: convert omap2_get_clksel to use new clksel struct

Convert omap2_get_clksel to use new struct clksel and struct
clksel_rate data.  Also fix its parameter order to conform with the
rest of the clock framework functions (i.e., struct clk first).

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>