msm: vidc: add active session check for clk and bus vote calculation

After couple of buffer transaction, sometimes session will be idle,
So do not consider inactive sessions for clk scaling and bus vote
calculation.

Change-Id: Ib4cc7606da6c828ce1d9108528a2cbbad4e5f6e4
Signed-off-by: Govindaraj Rajagopal <grajagop@codeaurora.org>