msm: kgsl: use the same logic in adreno_idle and adreno_isidle

These two functions need to agree on the meaning of "idle",
so that calling adreno_isidle() right after an adreno_idle()
will always return true.

Change-Id: I7cddf73773186c3ec8b56c111affacac3b07fcc7
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>
(cherry picked from commit 5365240cf0abf2d799dd849abca0dc5b46d4b784)
Signed-off-by: Harsh Vardhan Dwivedi <hdwivedi@codeaurora.org>

Signed-off-by: Sridhar Gujje <sgujje@codeaurora.org>