test: Run only the selected SPL test

Use the new -k option to select the test to run.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/py/tests/test_spl.py b/test/py/tests/test_spl.py
index 990cc9b..bd273da 100644
--- a/test/py/tests/test_spl.py
+++ b/test/py/tests/test_spl.py
@@ -24,7 +24,7 @@
     """
     try:
         cons = u_boot_console
-        cons.restart_uboot_with_flags(['-u', ut_spl_subtest])
+        cons.restart_uboot_with_flags(['-u', '-k', ut_spl_subtest.split()[1]])
         output = cons.get_spawn_output().replace('\r', '')
         assert 'Failures: 0' in output
     finally: