Removes the check for high command classes and instead checks that the
command classes needed are present.
Previous solution killed forward compatibility at no apparent gain.

Signed-of-by: Pierre Ossman <drzeus@drzeus.cx>

This patch only checks for CCC_BLOCK_READ even though CCC_BLOCK_WRITE is
also needed. My intention is to make the card read-only if the write
command class is unavailable. But such a patch will conflict with the SD
patches previously submitted. So I need to know which version should be
used as a base.