test/py: Use the correct fixture name in exception handler

If a BootFail exception is thrown in a test, it is not handled
correctly. Use the correct fixture variable 'ubman_fix' to resolve this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Fixes: d9ed4b75add ("test/py: Drop u_boot_ prefix on test files")
Reviewed-by: Mattijs Korpershoek <mkorpershoek@kernel.org>
1 file changed