msm: kgsl: Don't send same bus vote repeatedly

Currently, we keep sending the same bus vote endlessly. Fix that,
so that a bus vote is sent only if it was different than previous.

Change-Id: I93cd052daaee6d4e11c3c2f7cfe13ae23b3b3f44
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>