mmc: tmio: Use IS_ENABLED() to check for CONFIG_ option

Use IS_ENABLED() instead of CONFIG_IS_ENABLED() to check for CONFIG_
option which is identical across all of U-Boot and xPL builds.

Fixes: 2769ddc9 ("mmc: tmio: Replace ifdeffery with IS_ENABLED/CONFIG_IS_ENABLED macros")
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>