Many Colibri carrier boards are using 3.3V pull-up resistors on the
SD-Card connector. Letting it switch to 1.8V is an invalid state.

Do prevent this from happening by keeping the signaling voltage at 3.3V.
Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>