clk: msm: clock-rpm: Allocate memory for the last-vote optimization

A recent commit d7830d36 ("clk: msm: clock-rpm: Don't send unnecessary
RPM requests") introduced a regression on targets that use the new
dt-based clock controller, specifically MDM9640. The memory for the
last-vote is not allocated currently since the dt-based controller clock
structures are allocated at runtime. Fix this by also allocating memory
for the last-vote.

Change-Id: Ia8f08dc3bbf8d92dc0f56ee5d31c212ac9eb7ad0
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>
Signed-off-by: Smita Ghosh <smitag@codeaurora.org>