msm: kgsl: Fix message handling in hwsched hfi interrupt handler

Do not process HFI messages on the message queue in the interrupt
handler before interrupts are enabled on that queue. Otherwise, the
interrupt handler will read it off the queue, and then the inline
handler will not find any messages on the queue.

Change-Id: I569f29250c27a1a74e206489ad8234b2be39d448
Signed-off-by: Sushmita Susheelendra <ssusheel@codeaurora.org>