Update git submodules

* Update docs/submodules/policy/apex-pdp.git from branch 'master'
  to 53d016bd95ded26821a7711c6f049ffc4ccd51ca
  - correct a typo in doc APEX User Manual
    
    Issue-ID: POLICY-1523
    Change-Id: I44675a5119170ab724926ba08a3bfceefda31b57
    Signed-off-by: Hengye <yehui.wang@est.tech>
    
1 file changed