msm: clock-local: Adopt a more consistent variable name convention

Name variables of similar types that are used for similar purposes
with a consistent naming scheme. This makes the code easier to read
by eliminating confusion caused by variables with names like 'clk'
being used for 'struct clk' types in some functions, 'struct rcg_clk'
in others, 'struct branch_clk' in others, and so on.

Change-Id: Id53acda2a3872b640999126809ba1f76aaee85db
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>