Handle spurious wakeups in VerifyClass

Spurious wakeups in VerifyClass can cause the class status to be
the same as the old status. Relax the check to be >= to handle this.

Adding a regression test is infeasible since it is a hard to get a
thread in the "somebody else verifying" loop.

Test: test-art-host
Bug: 62912904
Change-Id: I308a395220507a875bb2fbf0800a14fabb434fda