clk: qcom: mdss: fix issue with gdsc vote

This change ensures that vote to turn on/off mdss gdsc is
balanced, so that gdsc can turn off in idle use cases.

Change-Id: I732d634b71013116773c87e3fb70e70c99dc3b13
Signed-off-by: Abhijit Kulkarni <kabhijit@codeaurora.org>