mmc: Fix printing of card DDR type

We should not call mmc_card_set_ddr_mode() if we are in single data
mode.  This sets DDR and causes the kernel log to say the card is DDR
when it is not.

Explicitly set ddr to 0 rather then rely on MMC_SDR_MODE being 0 when
doing the checks.

Signed-off-by: Philip Rakity <prakity@marvell.com>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Chris Ball <cjb@laptop.org>