mmc: davinci: fix unwinding in probe

Unwiding from an error in davinci_mmcsd_probe was a mess. Some errors were
not handled and not all paths unwound correctly. Also using devm_ where
possible to simplify things.

Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>