[ARM] pxa/cm-x300: fix mmc numbering

CM-X300 has libertas on mmc2 and  SD card slot on mmc1.
This patch fixes wrong MMC ports assignment.

Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>
Signed-off-by: Mike Rapoport <mike@compulab.co.il>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>