perf machine: Reuse module path buffer

perf machine: Reuse module path buffer

Rather than copying the path and appending the directory entry in a
fresh path buffer, append to the path at the end of where it is for
the recursion level. This saves a PATH_MAX buffer per recursion level
and some unnecessary copying.

Signed-off-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250222061015.303622-9-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>