msm: kgsl: Correct HFI acknowledgment failure condition

For generic requests, only 0xffffffff is an error code and all other
return codes are valid. Correct KGSL logic to reflect that.

Change-Id: I78d2bb9c3bcdfb1a0fe74aca5f3177e574988d7d
Signed-off-by: Mohammed Mirza Mandayappurath Manzoor <mmandaya@codeaurora.org>