NFS: Fix a compile issue in nfs_root

Stephen Rothwell reports:

> /home/test/linux-2.6/fs/nfs/nfsroot.c: In function 'nfs_root_debug':
> /home/test/linux-2.6/fs/nfs/nfsroot.c:110:2: error: 'nfs_debug'
> undeclared (first use in this function)
> /home/test/linux-2.6/fs/nfs/nfsroot.c:110:2: note: each undeclared
> identifier is reported only once for each function it appears in
> make[3]: *** [fs/nfs/nfsroot.o] Error 1
> make[2]: *** [fs/nfs] Error 2
> make[1]: *** [fs] Error 2
> make: *** [sub-make] Error 2

Which is caused by commit 306a0753
(NFS: Allow NFSROOT debugging messages to be enabled dynamically)

Fix is to disable this code when RPC_DEBUG is disabled.
Reported-by: NZimny Lech <napohybelskurwysynom2010@gmail.com>
Tested-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfsroot.c

@@ -101,6 +101,7 @@ static char nfs_export_path[NFS_MAXPATHLEN + 1] __initdata = "";
 /* server:export path string passed to super.c */
 static char nfs_root_device[NFS_MAXPATHLEN + 1] __initdata = "";
 
+#ifdef RPC_DEBUG
 /*
  * When the "nfsrootdebug" kernel command line option is specified,
  * enable debugging messages for NFSROOT.
@@ -112,6 +113,7 @@ static int __init nfs_root_debug(char *__unused)
 }
 
 __setup("nfsrootdebug", nfs_root_debug);
+#endif
 
 /*
  *  Parse NFS server and directory information passed on the kernel