clk: Squash __clk_{enable,disable}() into callers

These functions are only used in one place. Let's squash them
into their respective callers to save some lines.

Signed-off-by: Dong Aisheng <aisheng.dong@freescale.com>
[sboyd@codeaurora.org: Redo commit text, add NULL check in
clk_enable()]
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>