msm: clock: Migrate to prepare()/unprepare() APIs

Replace calls to clk_enable()/clk_disable() with calls to
clk_prepare_enable()/clk_unprepare_disable(). This is safe to do
because all these calls are made from non-atomic context.

Change-Id: I8bbb2c5df9a23796b808d4f882ffdb04319477ea
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>