Fix client creation failure in vr_hwc

There's some code in vr_hwc to prevent multiple clients, but it was
slightly broken in that only the first attempt to create a client would
work. If you destroyed the client and then tried to create another one,
it would incorrectly fail.

This results in a "failed to create composer client" assertion crash in
surface flinger the second time a user runs a vr app that uses vr
flinger.

Bug: 74985350

Test: Enable vr flinger render path, enter vr, exit vr, enter vr,
confirmed no crash.

Change-Id: Id5de0063c1e4e0be5a06d0a59b59ae3b669480f8