vt: convert last unbind_con_driver call to do_unbind_con_driver

There is only one place use unbind_con_driver, this patch
convert it to do_unbind_con_driver too, then we can delete
unbind_con_driver to reduce code size and duplication.
Signed-off-by: Wang YanQing <udknight@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/vt/vt.c

@@ -3303,8 +3303,11 @@ static int vt_unbind(struct con_driver *con)
 		if (first == 0 && last == MAX_NR_CONSOLES -1)
 			deflt = 1;
 
-		if (first != -1)
-			unbind_con_driver(csw, first, last, deflt);
+		if (first != -1) {
+			console_lock();
+			do_unbind_con_driver(csw, first, last, deflt);
+			console_unlock();
+		}
 
 		first = -1;
 		last = -1;