sh: disable SD-card write-protection detection on kfr2r09

kfr2r09 board has a micro-SD card slot, therefore card write-protection
detection cannot work there, disable it.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Ian Molton <ian@mnementh.co.uk>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>