iommu: pass cell_count = -1 to of_for_each_phandle with cells_name

Currently of_for_each_phandle ignores the cell_count parameter when a
cells_name is given. I intend to change that and let the iterator fall
back to a non-negative cell_count if the cells_name property is missing
in the referenced node.

To not change how existing of_for_each_phandle's users iterate, fix them
to pass cell_count = -1 when also cells_name is given which yields the
expected behaviour with and without my change.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Rob Herring <robh@kernel.org>