dmaengine: apple-admac: Fix grabbing of channels in of_xlate

[ Upstream commit 8454f880 ]

The of_xlate callback is supposed to return the channel after already
having 'grabbed' it for private use, so fill that in.

Fixes: b127315d

 ("dmaengine: apple-admac: Add Apple ADMAC driver")
Signed-off-by: Martin Povišer <povik+lin@cutebit.org>
Link: https://lore.kernel.org/r/20221019132324.8585-1-povik+lin@cutebit.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>