msm: kgsl: Fix spinlock corruption in hfi receiver

In case GMU failed to send back ACK to GMU driver on
CPU in time, GMU driver hfi message receiver shall
ignore the delayed ACK from GMU. The original request
message had been deleted by GMU driver. Handling
obsolete ACK could lead driver to use an invalid
spinlock structure in original request message.

CRs-Fixed: 2061912
Change-Id: I27a333950cb21c3832af201719ea16f8c0ce281d
Signed-off-by: George Shen <sqiao@codeaurora.org>