serial: s5p: Use IS_ENABLED where appropriate

There are no SPL/TPL variants of CONFIG_CLK_EXYNOS and
CONFIG_ARCH_APPLE, so switch from CONFIG_IS_ENABLED to
IS_ENABLED.

Signed-off-by: Mark Kettenis <kettenis@openbsd.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
1 file changed