msm: kgsl: Protect the bind object against bad dereference

Sparse bind object are unbinded with bind id. This
can be exploited by any malicious application calling
unbind with same bind id again and again.

This can lead to a race condition between two threads
where one free the bind object and second thread uses
same object leading to bad dereference.

Change-Id: I542a008fc647489560667fb5016453a0c3448f7a
Signed-off-by: Sunil Khatri <sunilkh@codeaurora.org>