perf tools: Use snprintf() in dso__read_running_kernel_build_id()

perf tools: Use snprintf() in dso__read_running_kernel_build_id()

dso__read_running_kernel_build_id() uses sprintf() to format a sysfs
path from machine->root_dir into a PATH_MAX buffer.  If root_dir is
close to PATH_MAX in length, appending "/sys/kernel/notes" (18 bytes)
overflows the stack buffer.

Switch to snprintf() with sizeof(path) to prevent the overflow.

Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Fixes: cdd059d731eeb466 ("perf tools: Move dso_* related functions into dso object")
Cc: Jiri Olsa <jolsa@kernel.org>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>