DMA-API: usb: ohci-sa1111: add a note about DMA masks

Add a comment to explain why this driver doesn't call any of the DMA
API dma_set_mask() functions.

Signed-off-by: Russell King <[e-mail]>

drivers/usb/host/ohci-sa1111.c

···
 	if (usb_disabled())
 		return -ENODEV;
 
+	/*
+	 * We don't call dma_set_mask_and_coherent() here because the
+	 * DMA mask has already been appropraitely setup by the core
+	 * SA-1111 bus code (which includes bug workarounds.)
+	 */
+
 	hcd = usb_create_hcd(&ohci_sa1111_hc_driver, &dev->dev, "sa1111");
 	if (!hcd)
 		return -ENOMEM;