Fix -Wextra warnings in frameworks/av/include

hardware/qcom/display includes frameworks/av/include headers
while compiling with -Wextra.  Fix warnings that were hidden
by -isystem.

Bug: 31751828
Test: lunch bullhead-userdebug && m -j checkbuild
Change-Id: Ib1ee7165882ff3cc1d85c123815604079483f725