ARM: shmobile: sh7372: sh7372_fsiXck_clk become non-global

FSI's external clock is controled by FSI driver.
Global sh7372_fsiXck_clk is no-longer needed now.

But it needs to set external clock rate by platform,
so, this patch supports clk_get() interface.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms@verge.net.au>