msm_serial_hs: Avoid RX getting stuck during rapid clock on/off

Due to race conditions in clock off and clock on sequence
BAM RX descriptor doesn't get queued or may get queued multiple
times. These issues may showup when the client issues rapid clock-on
clock-off operations.
This patch optimizes clock-off sequence while synchronizing clock
off/on with the BAM RX callback (In BAM RX callback, Forcestale
is not issued for every BAM RX callback).

CRs-Fixed: 601140
Change-Id: I882bb57b597f5789daa5fef33a4bc8da174110d0
Signed-off-by: Kiran Gunda <kgunda@codeaurora.org>