alsa_sound: Synchronization fix - standby and flush

-Standby was not waiting for DRAIN to finish before
calling standby on alsaHandle. Volume was also
not check AlsaHandle before calling it
-Fix this by adding lock and checking status of lock
CRs-Fixed: 493580

Change-Id: I318f5f120f4e02135e00962b670120f6000d49ef