mmc: call device_probe() after scanning

Every time a mmc bus/port is scanned and a new device is detected,
we want to call device_probe() as it will give us a chance to run
additional post-processings for some purposes.

In particular, support for creating partitions on a device will be added.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>