swiotlb: add comment where we handle the overflow of a dma mask on 32 bit

Impact: cleanup

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
1 file changed