dma-direct: don't truncate dma_required_mask to bus addressing capabilities

The dma required_mask needs to reflect the actual addressing capabilities
needed to handle the whole system RAM. When truncated down to the bus
addressing capabilities dma_addressing_limited() will incorrectly signal
no limitations for devices which are restricted by the bus_dma_mask.

Fixes: b4ebe606 (dma-direct: implement complete bus_dma_mask handling)
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Tested-by: Atish Patra <atish.patra@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

kernel/dma/direct.c

@@ -47,9 +47,6 @@ u64 dma_direct_get_required_mask(struct device *dev)
 {
 	u64 max_dma = phys_to_dma_direct(dev, (max_pfn - 1) << PAGE_SHIFT);
 
-	if (dev->bus_dma_mask && dev->bus_dma_mask < max_dma)
-		max_dma = dev->bus_dma_mask;
-
 	return (1ULL << (fls64(max_dma) - 1)) * 2 - 1;
 }