staging/lustre: silence gcc build warning

got bellow build warning that is indeed a false alarm.

  CC [M]  drivers/staging/lustre/lustre/llite/llite_nfs.o
  drivers/staging/lustre/lustre/libcfs/nidstrings.c: In function ‘
  libcfs_str2net_internal’:
  drivers/staging/lustre/lustre/libcfs/nidstrings.c:432:17: warning: ‘nf’ may be
  used uninitialized in this function [-Wuninitializ
  ed]

Signed-off-by: Peng Tao <tao.peng@emc.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>