ARM: dts: am335x-nano: Fix GPIO settings for MMC pins

The MMC slot uses GPIO pins for Write Protext and Card Detect.
Define these so everything works correctly.

Signed-off-by: Mark Jackson <mpfj@newflow.co.uk>
Message-Id: <20221130140547.295859-5-mpfj@newflow.co.uk>
Signed-off-by: Tony Lindgren <tony@atomide.com>