Revert "msm: kgsl: Do not decrease the KGSL open count"

This reverts commit e4d68fef.
Slumber has been verified to work on SDM845 so this is no
longer needed to prevent it.

CRs-Fixed: 2017390
Change-Id: I834f33a8f8d937229e262e08bfbf6db4d0d70a92
Signed-off-by: Kyle Piefer <kpiefer@codeaurora.org>