While the MMC handled the card's read only flag correctly on open,
it did not setup the flag in the allocated disk structure. The
consequence being that probing the /sys/class/block/mmcblkX/ro
attribute always reported 0.
Signed-off-by: Marc-Andre Hebert <hebert.marcandre@gmail.com> Reviewed-by: Chris Ball <cjb@laptop.org> Tested-by: Chris Ball <cjb@laptop.org> Signed-off-by: Chris Ball <cjb@laptop.org>