clk: mmp: add prefix "mmp" for structures defined for clk-frac

The structures defined for clk-frac will be used out side
of clk-frac.c.
To avoid conflicts, add prefix "mmp" for these structures'
name.

Signed-off-by: Chao Xie <chao.xie@marvell.com>
Acked-by: Haojian Zhuang <haojian.zhuang@gmail.com>
Signed-off-by: Michael Turquette <mturquette@linaro.org>