mmc: Correct definition of R6

During development of SDHC support, it was discovered that the definition
for R6 was incorrect. This patch fixes that and patches the drivers that
do switch on the response type.

Signed-off-by: Philip Langdale <philipl@overt.org>
Cc: Alex Dubov <oakad@yahoo.com>
Cc: Pavel Pisa <ppisa@pikron.com>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>