BaseMutex::IsExclusiveHeld should only be called on self.

Fix issue in Thread::DumpState of lock dumping calling IsExclusiveHeld on a
thread that isn't self causing intermittent crashes of ThreadStress oat test.

Bug: 15446488
Change-Id: I86924397a4e21ce10a95ea2a737d7bfbcb8ffe28
1 file changed