perf unwind: Fix uninitialized variable

The 'ret' variable may be uninitialized on error goto paths.

Fixes: dc2cf4ca

 ("perf unwind: Fix segbase for ld.lld linked objects")
Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
Reviewed-by: Fangrui Song <maskray@google.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM-14 (x86-64)
Cc: Fangrui Song <maskray@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: llvm@lists.linux.dev
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Ullrich <sebasti@nullri.ch>
Link: https://lore.kernel.org/r/20220607000851.39798-1-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>