mmc: cb710: fix #ifdef HAVE_EFFICIENT_UNALIGNED_ACCESS

HAVE_EFFICIENT_UNALIGNED_ACCESS is a config option, therefore it needs
the CONFIG_ before it when used by the preprocessor.

Signed-off-by: James Hogan <james@albanarts.com>
Acked-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Chris Ball <cjb@laptop.org>