The MODULE_LICENSE macro is missing from the kunit helpers file, thus
leading to a build error.

Let's introduce it along with MODULE_AUTHOR.

Fixes: 44a39283 ("drm/tests: Add Kunit Helpers")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reviewed-by: Maíra Canal <mairacanal@riseup.net>
Link: https://lore.kernel.org/r/20221116091712.1309651-2-maxime@cerno.techSigned-off-by: Maxime Ripard <maxime@cerno.tech>