sparse pointer use of zero as null

Get rid of sparse related warnings from places that use integer as NULL
pointer.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Cc: Andi Kleen <ak@suse.de>
Cc: Jeff Garzik <jeff@garzik.org>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Ian Kent <raven@themaw.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/ata/libata-sff.c b/drivers/ata/libata-sff.c
index 026439e..c750105 100644
--- a/drivers/ata/libata-sff.c
+++ b/drivers/ata/libata-sff.c
@@ -882,7 +882,7 @@
 	/* Filter out DMA modes if the device has been configured by
 	   the BIOS as PIO only */
 
-	if (adev->link->ap->ioaddr.bmdma_addr == 0)
+	if (adev->link->ap->ioaddr.bmdma_addr == NULL)
 		xfer_mask &= ~(ATA_MASK_MWDMA | ATA_MASK_UDMA);
 	return xfer_mask;
 }