tty: ipwireless: fix possible NULL dereference

The function alloc_ctrl_packet() can fail and return NULL. Incase it
fails print an error message and exit.
Signed-off-by: Sudip Mukherjee <sudip.mukherjee@codethink.co.uk>
Reviewed-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/ipwireless/hardware.c

@@ -1572,6 +1572,11 @@ static void handle_received_SETUP_packet(struct ipw_hardware *hw,
 					sizeof(struct ipw_setup_reboot_msg_ack),
 					ADDR_SETUP_PROT, TL_PROTOCOLID_SETUP,
 					TL_SETUP_SIGNO_REBOOT_MSG_ACK);
+			if (!packet) {
+				pr_err(IPWIRELESS_PCCARD_NAME
+				       ": Not enough memory to send reboot packet");
+				break;
+			}
 			packet->header.length =
 				sizeof(struct TlSetupRebootMsgAck);
 			send_packet(hw, PRIO_SETUP, &packet->header);