AMD/IOMMU: drop tasklet handler forward declaration

AMD/IOMMU: drop tasklet handler forward declaration

do_amd_iommu_irq()'s forward declaration uses a parameter name different
from what the definition uses, thus vioating Misra C:2012 rule 8.3. We
can get away without such a forward declaration if instead we forward-
declare amd_iommu_irq_tasklet, putting its initialization past the
handler function's definition.

No functional change.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>