Use accessor to read property serial numbers

Hide the implementation of the property structures by using
an accessor.

(cherry picked from commit 14c02f245e56687b765487d25a034d71196d33b6)

Change-Id: Id86ff99d8430fa73bbc745aaa0ff2b7713ca7885
Merge "Use accessor to read property serial numbers"
Merge https://android.googlesource.com/platform/hardware/libhardware_legacy into jb-devel