staging: btmtk_usb: check for a valid io_buf pointer

assigned to retval of kmalloc but not checked whether the allocation failed or not,
fail the registering if allocation fail
Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/btmtk_usb/btmtk_usb.c

@@ -1597,6 +1597,11 @@ static int btmtk_usb_probe(struct usb_interface *intf,
 	}
 
 	data->io_buf = kmalloc(256, GFP_ATOMIC);
+	if (!data->io_buf) {
+		hci_free_dev(hdev);
+		kfree(data);
+		return -ENOMEM;
+	}
 
 	btmtk_usb_switch_iobase(data, WLAN);