iommu/arm-smmu: Check for num_context_irqs > 0 to avoid divide by zero exception

With the right (or wrong;-) definition of v1 SMMU node in DTB it is
possible to trigger a division by zero in arm_smmu_init_domain_context
(if number of context irqs is 0):

       if (smmu->version == 1) {
               root_cfg->irptndx = atomic_inc_return(&smmu->irptndx);
 =>            root_cfg->irptndx %= smmu->num_context_irqs;
       } else {

Avoid this by checking for num_context_irqs > 0 when probing
for SMMU devices.

Change-Id: Ibfcb79abf05ea6c598a7fd6eff796cb23e82df33
Signed-off-by: Andreas Herrmann <andreas.herrmann@calxeda.com>
[will: changed to dev_err on probe failure path]
Signed-off-by: Will Deacon <will.deacon@arm.com>
Git-commit: 44a08de2aaf7f4cf86dfcf04bee32536e4a2b5b8
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>