mmc_spi: adjust for delayed data token response

Some cards are not able to send the data token in time, but
miss the time frame for some bits(!). So synchronize to the
start of the token.

Signed-off-by: Wolfgang Muees <wolfgang.mues@auerswald.de>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>