SATA: use NULL for ptrs

Fix sparse warnings in SATA:
drivers/ata/sata_sil.c:342:9: warning: Using plain integer as NULL pointer
drivers/ata/sata_mv.c:2056:55: warning: Using plain integer as NULL pointer

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/ata/sata_mv.c

@@ -2052,7 +2052,7 @@ static void mv_port_init(struct ata_ioports *port,  void __iomem *port_mmio)
 	port->altstatus_addr = port->ctl_addr = shd_base + SHD_CTL_AST_OFS;
 
 	/* unused: */
-	port->cmd_addr = port->bmdma_addr = port->scr_addr = 0;
+	port->cmd_addr = port->bmdma_addr = port->scr_addr = NULL;
 
 	/* Clear any currently outstanding port interrupt conditions */
 	serr_ofs = mv_scr_offset(SCR_ERROR);

drivers/ata/sata_sil.c

@@ -339,7 +339,7 @@ static inline void __iomem *sil_scr_addr(struct ata_port *ap, unsigned int sc_re
 		break;
 	}
 
-	return 0;
+	return NULL;
 }
 
 static u32 sil_scr_read (struct ata_port *ap, unsigned int sc_reg)