ARM: shmobile: Remove legacy clock support leftovers

The shmobile_clk_init() function has been removed and the linux/sh_clk.h
header doesn't need to be included anymore.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>