vt: Grab console_lock around con_is_bound in show_bind

Not really harmful not to, but also not harm in grabbing the lock. And
this shuts up a new WARNING I introduced in commit ddde3c1 ("vt:
More locking checks").

Reported-by: Jens Remus <jremus@linux.ibm.com>
Cc: linux-kernel@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: linux-fbdev@vger.kernel.org
Cc: linux-s390@vger.kernel.org
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Martin Hostettler <textshell@uchuujin.de>
Cc: Adam Borowski <kilobyte@angband.pl>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sam Ravnborg <sam@ravnborg.org>
Fixes: ddde3c1 ("vt: More locking checks")
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Tested-by: Jens Remus <jremus@linux.ibm.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://lore.kernel.org/r/20190718080903.22622-1-daniel.vetter@ffwll.ch
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/vt/vt.c

@@ -3771,7 +3771,11 @@ static ssize_t show_bind(struct device *dev, struct device_attribute *attr,
 			 char *buf)
 {
 	struct con_driver *con = dev_get_drvdata(dev);
-	int bind = con_is_bound(con->con);
+	int bind;
+
+	console_lock();
+	bind = con_is_bound(con->con);
+	console_unlock();
 
 	return snprintf(buf, PAGE_SIZE, "%i\n", bind);
 }