msm: kgsl: Retry rbbm batch register read

On a650, it's possible that a valid register read in the
batch register block inside rbbm may return 0xdeafbead. Retry
few times until you get back the actual register value.

Change-Id: I010899b876487fdcb61dfcfda89cc0c109735f72
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>