msm: kgsl: Fix race condition in adreno_spin_idle()

adreno_spin_idle spins for a timeout checking for gpu to idle.
Sometimes due to race conditions the timeout can occur before the
loop is executed. Change the logic to a do-while loop and add an
extra idle check after the timeout before returning failure.

CRs-Fixed: 978122
Change-Id: Idb92a0180dd8cc3e662b1ccf44d69e4bbafb29f1
Signed-off-by: Suman Tatiraju <sumant@codeaurora.org>