x86/iommu: Drop duplicate const in __IOMMU_INIT

It's redundant and makes sparse complain about it.

Signed-off-by: Mathias Krause <minipli@googlemail.com>
Cc: Joerg Roedel <joerg.roedel@amd.com>
Link: http://lkml.kernel.org/r/1346621506-30857-7-git-send-email-minipli@googlemail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>