NFS: Remove unneeded NFS_DEBUG checking before define NFSDBG_FACILITY

It's not needed to checking NFS_DEBUG before define NFSDBG_FACILITY, remove it.

Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>