[ProfileData] Report errors from InstrProfSymtab::create

InstrProfSymtab::create can fail with instrprof_error::malformed, but
this error is silently dropped. Propagate the error up to the caller so
we fail early.

Eventually, I'd like to transition ProfileData over to the new Error
class so we can't ignore hard failures like this.

llvm-svn: 267055