msm: footswitch: Move to new clock APIs

What was once done by just clk_enable() is being split into two
functions: clk_prepare() and clk_enable(), where the prepare
function may sleep but the enable function will not. The same
is true for the clk_disable() function.

Replace use of clk_enable() and clk_disable() with calls to
clk_prepare_enable() and clk_disable_unprepare(), respectively.
These macros are combinations of the APIs described above and
are safe to use in the footswitch driver since they are not
called from atomic context.

Change-Id: Ic51e17304f0a046d213226b1e93c7f71ef3d9a9b
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>