perf test trace+probe_vfs_getname.sh: Remove stray \ before /

perf test trace+probe_vfs_getname.sh: Remove stray \ before /

Running on fedora:38 in verbose mode I noticed:

  # perf test -v 117
  grep: warning: stray \ before /
  117: Check open filename arg using perf trace + vfs_getname          :

Remove that \ before /.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/lkml/ZNvTDsSMO3nw9Tnp@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>