Bluetooth: ath3k: fix checkpatch warning

This patch fixed warning:
 WARNING: Prefer using '"%s...", __func__' to using 'ath3k_disconnect', this function's name, in a string
 #568: FILE: drivers/bluetooth/ath3k.c:568:
 +	BT_DBG("ath3k_disconnect intf %p", intf);

Signed-off-by: Maxim Zhukov <mussitantesmortem@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>