msm: vidc: Fix to avoid setting TURBO flag when load is 0

Avoid setting power mode with TURBO flag when the session
is in invalid state or the load is zero to avoid setting
bus voting to max frequency.

Change-Id: Ibc93c42a9642f6af7f7af85a1ac7d171684d5970
Signed-off-by: Mahesh Voorugonda <mvooru@codeaurora.org>