staging: comedi: ni_atmio: make device_ids const

The `device_ids[]` passed to `MODULE_DEVICE_TABLE()` should be `const`.
When the "ni_atmio" driver is built-in, gcc warns about `device_ids`
being defined but ununsed.  Make it `const`.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/ni_atmio.c

@@ -216,7 +216,7 @@ static const int ni_irqpin[] = {
 
 #include "ni_mio_common.c"
 
-static struct pnp_device_id device_ids[] = {
+static const struct pnp_device_id device_ids[] = {
 	{.id = "NIC1900", .driver_data = 0},
 	{.id = "NIC2400", .driver_data = 0},
 	{.id = "NIC2500", .driver_data = 0},