msm: kgsl: Fix the refcounting on the A6XX context record

The user context record had an extra refcount, preventing it from
being destroyed. Fix the refcounting.

Change-Id: Iafb86f40a9898ee41e4d80880192ced2d21c82cb
Signed-off-by: Lynus Vaz <lvaz@codeaurora.org>
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>