vt: fix old keyboard release in CONS_SETKBD

On the first switch we previously released the newly allocated keyboard
instead of the old one. Keyboard state was very confused afterwards for
further keyboard switches.

Submitted by:	bde

sys/dev/vt/vt_core.c

@@ -2359,6 +2359,7 @@ skip_thunk:
 			    (void *)vd, vt_kbdevent, vd);
 			if (i >= 0) {
 				if (vd->vd_keyboard != -1) {
+					kbd = kbd_get_keyboard(vd->vd_keyboard);
 					vt_save_kbd_state(vd->vd_curwindow, kbd);
 					kbd_release(kbd, (void *)vd);
 				}