fs/nfs: fix new compiler warning about boolean in switch

The brand new GCC 5.1.0 warns by default on using a boolean in the
switch condition. This results in the following warning:

fs/nfs/nfs4proc.c: In function 'nfs4_proc_get_rootfh':
fs/nfs/nfs4proc.c:3100:10: warning: switch condition has boolean value [-Wswitch-bool]
  switch (auth_probe) {
          ^

This code was obviously using switch to make use of the fall-through
semantics (without the usual comment, though).
Rewrite that code using if statements to avoid the warning and make
the code a bit more readable on the way.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/nfs4proc.c

@@ -3096,16 +3096,13 @@ int nfs4_proc_get_rootfh(struct nfs_server *server, struct nfs_fh *fhandle,
 			 struct nfs_fsinfo *info,
 			 bool auth_probe)
 {
-	int status;
+	int status = 0;
 
-	switch (auth_probe) {
-	case false:
+	if (!auth_probe)
 		status = nfs4_lookup_root(server, fhandle, info);
-		if (status != -NFS4ERR_WRONGSEC)
-			break;
-	default:
+
+	if (auth_probe || status == NFS4ERR_WRONGSEC)
 		status = nfs4_do_find_root_sec(server, fhandle, info);
-	}
 
 	if (status == 0)
 		status = nfs4_server_capabilities(server, fhandle);