amd-iommu: set evt_buf_size correctly

The setting of this variable got lost during the suspend/resume
implementation.  But keeping this variable zero causes a divide-by-zero
error in the interrupt handler. This patch fixes this.
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

arch/x86/kernel/amd_iommu_init.c

@@ -472,6 +472,8 @@ static u8 * __init alloc_event_buffer(struct amd_iommu *iommu)
 	if (iommu->evt_buf == NULL)
 		return NULL;
 
+	iommu->evt_buf_size = EVT_BUFFER_SIZE;
+
 	return iommu->evt_buf;
 }