test: sharpen button label unit test

Using different strings for the device tree node labels and the label
property of buttons sharpens the button label unit test.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Philippe Reynes <philippe.reynes@softathome.com>
diff --git a/test/py/tests/test_button.py b/test/py/tests/test_button.py
index 98067a9..eadd9dd 100644
--- a/test/py/tests/test_button.py
+++ b/test/py/tests/test_button.py
@@ -11,7 +11,7 @@
     expected_response = 'rc:0'
     response = u_boot_console.run_command('button list; echo rc:$?')
     assert(expected_response in response)
-    response = u_boot_console.run_command('button summer; echo rc:$?')
+    response = u_boot_console.run_command('button button1; echo rc:$?')
     assert(expected_response in response)
 
     expected_response = 'rc:1'