ACPI: Fix sparse warnings

Use NULL for pointers

drivers/acpi/osl.c:208:10: warning: Using plain integer as NULL pointer
drivers/acpi/tables/tbxface.c:411:49: warning: Using plain integer as NULL pointer
drivers/acpi/processor_core.c:1008:10: warning: Using plain integer as NULL pointer

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Len Brown <len.brown@intel.com>
diff --git a/drivers/acpi/tables/tbxface.c b/drivers/acpi/tables/tbxface.c
index 807978d..8193700 100644
--- a/drivers/acpi/tables/tbxface.c
+++ b/drivers/acpi/tables/tbxface.c
@@ -408,7 +408,7 @@
 		}
 
 		if (!acpi_gbl_permanent_mmap) {
-			acpi_gbl_root_table_list.tables[i].pointer = 0;
+			acpi_gbl_root_table_list.tables[i].pointer = NULL;
 		}
 
 		return (status);