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 <[e-mail]>
Reviewed-by: Jiri Kosina <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/ipwireless/hardware.c

···
 					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);