iommu: iommu-debug: Fix input IOVA usage in atos_write()

atos_write() uses the IOVA stored in the debug device structure
for translating the input IOVA to a physical address, which is
not correct, given that the debug device structure's IOVA field
has not been initialized yet. Use the IOVA given as an input
for translating the IOVA to a physical address.

Change-Id: I7a8f241abc573fcf877147ca4d808c025cbb45f9
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>