clk: shmobile: fix setting paretn clock rate

If the driver needs to change a clock rate, then it must be propogated
through the MSTP clock to the parent clock (such as shdi0 -> sd0). Without
this we cannot up-rate default clocks which are really slow (such as the
mmcif1 which defaults to 12MHz where it could be running at 97MHz)

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>