test: Adjust the of-platdata test run condition

This should be spl_of_platdata, since otherwise it will try to run on boards
that don't support of-platdata.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/py/tests/test_ofplatdata.py b/test/py/tests/test_ofplatdata.py
index c8b309e..457c405 100644
--- a/test/py/tests/test_ofplatdata.py
+++ b/test/py/tests/test_ofplatdata.py
@@ -34,7 +34,7 @@
 stringarray "one" "" ""
 '''
 
-@pytest.mark.buildconfigspec('spl')
+@pytest.mark.buildconfigspec('spl_of_platdata')
 def test_ofplatdata(u_boot_console):
     """Test that of-platdata can be generated and used in sandbox"""
     cons = u_boot_console