Bluetooth: Fix warning: variable 'tty' set but not used

The patch below fixes a warning message when using gcc 4.6.0.

  CC [M]  drivers/bluetooth/hci_ldisc.o
drivers/bluetooth/hci_ldisc.c: In function 'hci_uart_send_frame':
drivers/bluetooth/hci_ldisc.c:213:21: warning: variable 'tty' set but not used

Signed-off-by: Justin P. Mattock <justinmattock@gmail.com>
Reviewed-By: Gustavo F. Padovan <gustavo@padovan.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>