msm: synx: protect clean up with mutex lock

While cleaning up synx table entry, hold the lock for that particular
entry. This will make sure that any other read/write for same entry waits
till cleaning is done.

Also, Change log level of empty table entries from warning to debug.

Change-Id: Ib092f41a12fb943ed184c031dca481a75d3446e3
Signed-off-by: Ram Nagesh <quic_ramnages@quicinc.com>