Proper fix for vr_wm: the hwc_callback function is no longer called

Another change removed the call to GetBufferFromHandle but didn't
delete it and an alternate implementation is used. This replicates
the change into the second implementation and removes the original one

Bug: None
Test: Tested in dev branch; built in master
Change-Id: I2bdb38c7b692e30cf1b5e41476ecdd062b5d5d69