msm: kgsl: Remove guard band on HFI message queues

The 16 byte guard band was introduced to give warm fuzzies
to ensure that KMD doesn't corrupt neighboring HFI queues.
This is not needed so keep our math simple and remove the
guard band between queues.

Change-Id: Iea7b02fd48332c644e3368905bafbe3b098cae8d
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>