mmc: core: Fix voltage select in DDR mode

This patch fixes the wrong comparison before setting the interface
voltage in DDR mode.

The assignment to the variable ddr before comaprison is either
ddr = MMC_1_2V_DDR_MODE; or ddr == MMC_1_8V_DDR_MODE. But the comparison
is done with the extended csd value if ddr == EXT_CSD_CARD_TYPE_DDR_1_2V.

Signed-off-by: Girish K S <girish.shivananjappa@linaro.org>
Acked-by: Subhash Jadavani <subhashj@codeaurora.org>
Acked-by: Philip Rakity <prakity@marvell.com>
Cc: <stable@kernel.org>
Signed-off-by: Chris Ball <cjb@laptop.org>