mmc: Remove return from mmc_init for non SD 2.0 compatible cards.

Cards which are not compatible with SD 2.0 standard, may return response
for CMD8 command, but it will be invalid in terms of SD 2.0. We should
accept this case as admissible, just like Linux does.

Signed-off-by: Yauhen Kharuzhy <jekhor@gmail.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>