RATIONAL_KUNIT_TEST selects RATIONAL, thus enabling an optional feature
the user may not want to have enabled.  Fix this by making the test depend
on RATIONAL instead.

Link: https://lkml.kernel.org/r/20210706100945.3803694-3-geert@linux-m68k.org
Fixes: b6c75c4a ("lib/math/rational: add Kunit test cases")
Signed-off-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Brendan Higgins <brendanhiggins@google.com>
Cc: Colin Ian King <colin.king@canonical.com>
Cc: Trent Piepho <tpiepho@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>