ACPI/IORT: Fix build when CONFIG_IOMMU_API=n

ACPI/IORT: Fix build when CONFIG_IOMMU_API=n

Commit 8097e53eaba2 ("ACPI/IORT: Use helper functions to access
dev->iommu_fwspec") changed by mistake the iort_fwspec_iommu_ops() stub
definition (compiled in when CONFIG_IOMMU_API=n), that caused the
following compilation failure:

drivers/acpi/arm64/iort.c:880:1: error: expected identifier or
'(' before '{' token
 { return NULL; }
 ^
drivers/acpi/arm64/iort.c:879:39: warning: 'iort_fwspec_iommu_ops'
used but never defined
 static inline const struct iommu_ops *iort_fwspec_iommu_ops(struct device *dev);
                                       ^~~~~~~~~~~~~~~~~~~~~

Fix it.

Fixes: 8097e53eaba2 ("ACPI/IORT: Use helper functions to access dev->iommu_fwspec")
Signed-off-by: Qian Cai <cai@lca.pw>
[lorenzo.pieralisi@arm.com: updated tags and log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Hanjun Guo <hanjun.guo@linaro.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Will Deacon <will.deacon@arm.com>