mmc: core: Use device_property_read instead of of_property_read

Using the device_property interfaces allows mmc drivers to work
on platforms which run on either device tree or ACPI.

Signed-off-by: David Woods <dwoods@mellanox.com>
Reviewed-by: Chris Metcalf <cmetcalf@mellanox.com>
Cc: stable@vger.linux.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>