use DMA_BIT_MASK instead of inline constant

Use DMA_BIT_MASK(24) instead of 0x00ffffff in DMA-mapping.txt
Signed-off-by: NMarin Mitov <mitov@issp.bas.bg>
Signed-off-by: NRandy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Documentation/DMA-mapping.txt

@@ -214,7 +214,7 @@ most specific mask.
 Here is pseudo-code showing how this might be done:
 
 	#define PLAYBACK_ADDRESS_BITS	DMA_BIT_MASK(32)
-	#define RECORD_ADDRESS_BITS	0x00ffffff
+	#define RECORD_ADDRESS_BITS	DMA_BIT_MASK(24)
 
 	struct my_sound_card *card;
 	struct pci_dev *pdev;