asm/clk.h was included get_peripheral_clk_rate function. But this
is not used from anywhere.
This removed asm/clk.h, and deleted include line from arch/sh/lib/time.c

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>