Fix BufferHubBufferTest test crash

Fix: 124377165
Test: BufferHub_test
verified on vega_xr target on oc-dr1-daydream-dev branch.
I cannot reproduce the test failure on master branch locally, although
it exist on the builds on Blackbox dashboard. Anyhow, I am certain about
this fix.

Change-Id: Ic473aae794b2996da1e713cd02a2bfc31cbaab1b