C2Fence: properly handle signal interruption of pipe fence wait

PipeFenceImpl::wait can be interrupted by signals. We used to
return C2_CANCELED which is not allowed by the spec. Instead,
retry wait until timeout.

Bug: 372561097
Flag: EXEMPT bugfix
Test: presubmit
Change-Id: I3907b8118aba6302b4fa816994e5d6be386d86e7