clk: msm: clock-alpha-pll: Update handoff for dynamic alpha pll

Current handoff of alpha pll does not store the current VCO mode
for slewing pll. Calculate and store the VCO mode during handoff
for slewing PLL, so as to avoid PLL disable and reconfiguration
during the set rate.

Change-Id: I765bf9c3cbf0ae745f32a5eed157e10307a94e03
Signed-off-by: Odelu Kukatla <okukatla@codeaurora.org>