msm: gsi: gsi channel mode switch spinlock correction

Revert the unnecessary change we made on spinlock, revert
the wrong change from WARN_ON to BUG we made on msm-4.14
when propagte from msm-4.9 branch which will cause the
false-alarm when we are switching to polling mode after
suspend

Change-Id: Id8daf86071d0a91ad0ecf6880be042abdb02a494
Signed-off-by: Bojun Pan <bojunp@codeaurora.org>