mmc: jz4740: Fix error exit path in driver's probe

Currently, if jz4740_mmc_request_gpios() fails, the driver
tries to release DMA resources. This is wrong because DMA
is requested at a later stage.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
[Ezequiel: cleanup commit message]
Tested-by: Mathieu Malaterre <malat@debian.org>
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.co.uk>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>