staging/lustre/ptlrpc: Fix ENABLE_PINGER ifdef

As it is ENABLE_PINGER is never defined, but in reality
it's the code that is now compiled out that should be used
since all other instances were converted like that too.

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>