swiotlb: fix comment on swiotlb_bounce()

swiotlb: fix comment on swiotlb_bounce()

Fix the comment as swiotlb_bounce() is used to copy from original dma
location to swiotlb buffer during swiotlb_tbl_map_single(), while to
copy from swiotlb buffer to original dma location during
swiotlb_tbl_unmap_single().

Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Orabug: 29582587
(cherry picked from commit 6442ca2abf882d9d838fb844d852ba6acd1db7f4)

Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>