mmc: tmio: remove stale comments

These don't make sense anymore. Since commit 5d60e500 ("mmc: tmio:
add new TMIO_MMC_HAVE_HIGH_REG flags"), we don't deal with a resource
here.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>