omap2 clock: remove all {src, rate}_offset fields from struct clk

src_offset and rate_offset are no longer used in OMAP2 clock framework
after the struct clksel/struct clksel_rate additions.  Remove these
fields from clock.h and #ifdef out those fields for OMAP24XX compiles.

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