Input: tests - modular KUnit tests should not depend on KUNIT=y

Input: tests - modular KUnit tests should not depend on KUNIT=y

While KUnit tests that cannot be built as a loadable module must depend
on "KUNIT=y", this is not true for modular tests, where it adds an
unnecessary limitation.

Fix this by relaxing the dependency to "KUNIT".

Fixes: fdefcbdd6f361841 ("Input: Add KUnit tests for some of the input core helper functions")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://lore.kernel.org/r/483c4f520e4acc6357ebba3e605977b4c56374df.1683022164.git.geert+renesas@glider.be
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>