cifs: free nativeFileSystem field before allocating a new one

...otherwise, we'll leak this memory if we have to reconnect (e.g. after
network failure).
Signed-off-by: Jeff Layton <jlayton@redhat.com>
CC: Stable <stable@kernel.org>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/connect.c

@@ -2726,6 +2726,7 @@ CIFSTCon(unsigned int xid, struct cifsSesInfo *ses,
 		strncpy(tcon->treeName, tree, MAX_TREE_SIZE);
 
 		/* mostly informational -- no need to fail on error here */
+		kfree(tcon->nativeFileSystem);
 		tcon->nativeFileSystem = cifs_strndup_from_ucs(bcc_ptr,
 						      bytes_left, is_unicode,
 						      nls_codepage);