cifs: convert prefixpath delimiters in cifs_build_path_to_root

Regression from 2.6.39...

The delimiters in the prefixpath are not being converted based on
whether posix paths are in effect. Fixes:

    https://bugzilla.redhat.com/show_bug.cgi?id=727834Reported-and-Tested-by: Iain Arnell <iarnell@gmail.com>
Reported-by: Patrick Oltmann <patrick.oltmann@gmx.net>
Cc: Pavel Shilovsky <piastryyy@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/inode.c

@@ -764,20 +764,10 @@ char *cifs_build_path_to_root(struct smb_vol *vol, struct cifs_sb_info *cifs_sb,
 	if (full_path == NULL)
 		return full_path;
 
-	if (dfsplen) {
+	if (dfsplen)
 		strncpy(full_path, tcon->treeName, dfsplen);
-		/* switch slash direction in prepath depending on whether
-		 * windows or posix style path names
-		 */
-		if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_POSIX_PATHS) {
-			int i;
-			for (i = 0; i < dfsplen; i++) {
-				if (full_path[i] == '\\')
-					full_path[i] = '/';
-			}
-		}
-	}
 	strncpy(full_path + dfsplen, vol->prepath, pplen);
+	convert_delimiter(full_path, CIFS_DIR_SEP(cifs_sb));
 	full_path[dfsplen + pplen] = 0; /* add trailing null */
 	return full_path;
 }