Fix BufferHubMetadata_test build on oc branch

By some reason in master branch the compiler could find unique_fd.h on
compiling, but in oc-dr1-daydream-dev it's complaining about it.

Test: m BufferHubMetadata -j (build passed)
Bug: none
Change-Id: I26e3e5288ec60f2c3d11d8416e563ef074eb553c