isdn/gigaset: use gig_dbg() for debugging output

The "TTY buffer in tty_port" patchset introduced an opencoded
debug message in the Gigaset tty device if_close() function.
Change it to use the gig_dbg() macro like everywhere else in
the driver.

Signed-off-by: Tilman Schmidt <tilman@imap.cc>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/isdn/gigaset/interface.c

@@ -176,7 +176,7 @@ static void if_close(struct tty_struct *tty, struct file *filp)
 	struct cardstate *cs = tty->driver_data;
 
 	if (!cs) { /* happens if we didn't find cs in open */
-		printk(KERN_DEBUG "%s: no cardstate\n", __func__);
+		gig_dbg(DEBUG_IF, "%s: no cardstate", __func__);
 		return;
 	}