Fix asserts for GetReadbackBufferFenceInactive

If there's no readback buffer, then the status is NOT ok(), and the
returned fence must be -1.

Bug: 213493262
Test: VtsHalGraphicsComposer3_TargetTest
Change-Id: Iff1b6e04126bfcc748f0f8d173f63244bfd83be4
1 file changed