msm: kgsl: Do not read retry RBBM register read

For A650v1 a valid RBBM register read could be 0xdeafbead.
This is fixed in A650v2.1 so do not attempt to read
the registers multiple times.

Change-Id: Ifae1a3513097e041275f09a64308a816de4e50f1
Signed-off-by: Urvashi Agrawal <urvaagra@codeaurora.org>