iommu/amd: Fix section mismatch warning

The variable amd_iommu_pre_enabled is used in non-init
code-paths, so remove the __initdata annotation.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Fixes: 3ac3e5ee ('iommu/amd: Copy old trans table from old kernel')
Acked-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>