dma-mapping: use dma_get_mask in dma_addressing_limited

We currently have cases where the dma_addressing_limited() gets
called with dma_mask unset. This causes a NULL pointer dereference.

Use dma_get_mask() accessor to prevent the crash.

Fixes: b8664554

 ("dma-mapping: add a dma_addressing_limited helper")
Signed-off-by: Eric Auger <eric.auger@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>