mmc_spi: do not check CID and CSD blocks with CRC16

Some cards are not able to calculate a valid CRC16 value
for CID and CSD reads (CRC for 512 byte data blocks is OK).
By moving the CRC enable after the read of CID and CSD, these
cards can be used. This patch was tested with a faulty 8 GByte
takeMS Class 6 SDHC card. This patch was suggested by
Pierre Ossman.

Signed-off-by: Wolfgang Muees <wolfgang.mues@auerswald.de>
Signed-off-by: Pierre Ossman <pierre@ossman.eu>