iommu/apple-dart: fix device leak on of_xlate()

iommu/apple-dart: fix device leak on of_xlate()

commit a6eaa872c52a181ae9a290fd4e40c9df91166d7a upstream.

Make sure to drop the reference taken to the iommu platform device when
looking up its driver data during of_xlate().

Fixes: 46d1fb072e76 ("iommu/dart: Add DART iommu driver")
Cc: stable@vger.kernel.org	# 5.15
Cc: Sven Peter <sven@kernel.org>
Acked-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>