libbpf-tools: Fix a compiler warning on oomkill
libbpf-tools: Fix a compiler warning on oomkill

oomkill.c: In function ‘handle_event’:
oomkill.c:49:12: warning: ‘n’ may be used uninitialized in this function [-Wmaybe-uninitialized]
   49 |         if (n)
      |            ^

iovisor/bcc,iovisor/bcc,iovisor/bcc,iovisor/bcc,iovisor/bcc