msm: clock-local: Rename __branch_clk_*_reg() to __branch_*_reg()

Having "branch_clk" in the names of these functions in inappropriate
since they operate on branches, regardless of whether they are part
of a branch_clk, rcg_clk, cdiv_clk, etc.

Change-Id: Id06d31034405f98352d519d500e22f05cb78e267
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>