iommu/arm-smmu: check return value of register_smmu_master

We currently don't check whether register_smmu_master while parsing the
device tree and adding device masters. Add error checking to facilitate
debugging and avoid probing of bogus devices.

Change-Id: I79c70d193c4705c21ea6a2e03ee048e7a4813b71
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>