qdsp5: audio: Set audio stopped flag before calling wakeup

During audio flush and stop command processing, wakeup on read
and write wait queue is done first and then audio stopped flag
is set to true. If a process waiting on read and write queue gets
scheduled first before stopped flag is set then this may result in
read or write command being sent to DSP after adsp disable operation,
which is unexpected.

Fix this by setting stopped flag before calling wakeup.

Change-Id: I20ef197e572d0ffc015d6004296ea7b9f5db2806
Signed-off-by: Manish Dewangan <manish@codeaurora.org>