staging: comedi: tests: ni_routes_test: Fix compilation error

The `ni_routes_test` module is not currently selectable using the
Kconfig files, but can be built by specifying `CONFIG_COMEDI_TESTS=m` on
the "make" command line.  It currently fails to compile due to an extra
parameter added to the `ni_assign_device_routes` function by
commit e3b7ce73 ("staging: comedi: ni_routes: Allow alternate board
name for routes").  Fix it by supplying the value `NULL` for the added
`alt_board_name` parameter (which specifies that there is no alternate
board name).

Fixes: e3b7ce73 ("staging: comedi: ni_routes: Allow alternate board name for routes")
Cc: Spencer E. Olson <olsonse@umich.edu>
Signed-off-by: NIan Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20210407140142.447250-2-abbotti@mev.co.ukSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/tests/ni_routes_test.c

@@ -217,7 +217,8 @@ void test_ni_assign_device_routes(void)
 	const u8 *table, *oldtable;
 
 	init_pci_6070e();
-	ni_assign_device_routes(ni_eseries, pci_6070e, &private.routing_tables);
+	ni_assign_device_routes(ni_eseries, pci_6070e, NULL,
+				&private.routing_tables);
 	devroutes = private.routing_tables.valid_routes;
 	table = private.routing_tables.route_values;
 
@@ -253,7 +254,8 @@ void test_ni_assign_device_routes(void)
 	olddevroutes = devroutes;
 	oldtable = table;
 	init_pci_6220();
-	ni_assign_device_routes(ni_mseries, pci_6220, &private.routing_tables);
+	ni_assign_device_routes(ni_mseries, pci_6220, NULL,
+				&private.routing_tables);
 	devroutes = private.routing_tables.valid_routes;
 	table = private.routing_tables.route_values;