perf probe: Add missing 0x prefix for addresses printed in hexadecimal

To fix this confusing warning:

  # perf probe -l
  Failed to find debug information for address 798240
    probe_main:prometheus_new_counter__return (on github.com/prometheus/client_golang/prometheus.NewCounter%return in /home/acme/git/prometheus-uprobes/main with counter)
  #

As that 798240 is printed with PRIx64 but has no letters, better print
the 0x prefix to disambiguate.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/lkml/ZEBCyFu2GjTw6qOi@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>