mmc: mxs-mmc: Fix a resource leak in an error handling path in 'mxs_mmc_probe()'

If 'mmc_of_parse()' fails, we must undo the previous 'dma_request_chan()'
call.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/20201208203527.49262-1-christophe.jaillet@wanadoo.fr


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