clk: msm: hdmi: correct the precision when calculating HDMI PLL

In existing HDMI PLL driver the VCO frequency value is truncated
so following PLL calculation could be impacted. Use 64 bit value
instead to maintain the necessary precision.

CRs-Fixed: 1086894
Change-Id: Iec3f65942dd152b0b7aa32af1a90039fff06cb34
Signed-off-by: Ray Zhang <rayz@codeaurora.org>