cifs: allow calling cifs_build_path_to_root on incomplete cifs_sb

It's possible that cifs_mount will call cifs_build_path_to_root on a
newly instantiated cifs_sb. In that case, it's likely that the
master_tlink pointer has not yet been instantiated.

Fix this by having cifs_build_path_to_root take a cifsTconInfo pointer
as well, and have the caller pass that in.

Reported-and-Tested-by: Robbert Kouprie <robbert@exx.nl>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 387b91a..cc1a860 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -2833,7 +2833,7 @@
 	/* check if a whole path (including prepath) is not remote */
 	if (!rc && cifs_sb->prepathlen && tcon) {
 		/* build_path_to_root works only when we have a valid tcon */
-		full_path = cifs_build_path_to_root(cifs_sb);
+		full_path = cifs_build_path_to_root(cifs_sb, tcon);
 		if (full_path == NULL) {
 			rc = -ENOMEM;
 			goto mount_fail_check;