mmc: owl-mmc: Fix a resource leak in an error handling path and in the remove function

mmc: owl-mmc: Fix a resource leak in an error handling path and in the remove function

'dma_request_chan()' calls should be balanced by a corresponding
'dma_release_channel()' call.

Add the missing call both in the error handling path of the probe function
and in the remove function.

Fixes: ff65ffe46d28 ("mmc: Add Actions Semi Owl SoCs SD/MMC driver")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/20201209194202.54099-1-christophe.jaillet@wanadoo.fr
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>