msm: kgsl: Use adreno_read_gmureg to read GMU registers

When the GMU is enabled, we must use the adreno_read_gmureg
function to read the GMU_ALWAYSON registers.

Change-Id: I87badfd3026087b8bc8b2219841b1d64e6ddb979
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>
Signed-off-by: Kyle Piefer <kpiefer@codeaurora.org>