msm: kgsl: Change polling to use do while loop

In rare cases, a polling loop could be skipped over due
to the timeout already being expired when the loop starts.
This could happen due to preemption, and causes the
function to fail. Change the function to use a do while
instead of a while so the register is always read at least
once even if the timeout is expired.

CRs-Fixed: 2017390
Change-Id: I7b4e66a7fa863615c7393108ec6b1f4f0978adc2
Signed-off-by: Kyle Piefer <kpiefer@codeaurora.org>