msm: clock-voter: Assign voter_clk_handoff() in clk_ops_voter

voter_clk_handoff() was never assigned as the handoff op for
clk_ops_voter. Fix this and mark it as static at the same time.

Change-Id: I8d6ff1eea35a7e57aeb0be220c1e80d43a923722
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>