perf debug: Avoid stack overflow in recursive error message

In debug_file, pr_warning_once is called on error. As that function
calls debug_file the function will yield a stack overflow. Switch the
location of the call so the recursion is avoided.

Reviewed-by: Howard Chu <howardchu95@gmail.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Reviewed-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: https://lore.kernel.org/r/20250228222308.626803-2-irogers@google.com


Fixes: ec49230c ("perf debug: Expose debug file")
Signed-off-by: Namhyung Kim <namhyung@kernel.org>