mmc: block: Use dev_set|get_drvdata()

In most of the cases mmc_get|set_drvdata() didn't simplify code, which
should be the primary reason for such macros.

Let's remove them and convert to the common device_driver macros,
dev_set|get_drvdata() instead.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>