x86: ds.c ptrace.c integer as NULL pointer sparse fixes

fix:

 arch/x86/kernel/ptrace.c:763:29: warning: Using plain integer as NULL pointer
 arch/x86/kernel/ptrace.c:777:46: warning: Using plain integer as NULL pointer
 arch/x86/kernel/ptrace.c:1115:45: warning: Using plain integer as NULL pointer
 arch/x86/kernel/ds.c:482:26: warning: Using plain integer as NULL pointer
 arch/x86/kernel/ds.c:487:25: warning: Using plain integer as NULL pointer

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Acked-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/kernel/ds.c b/arch/x86/kernel/ds.c
index ab21c27..2b69994 100644
--- a/arch/x86/kernel/ds.c
+++ b/arch/x86/kernel/ds.c
@@ -479,12 +479,12 @@
 		goto out;
 
 	kfree(context->buffer[qual]);
-	context->buffer[qual] = 0;
+	context->buffer[qual] = NULL;
 
 	current->mm->total_vm  -= context->pages[qual];
 	current->mm->locked_vm -= context->pages[qual];
 	context->pages[qual] = 0;
-	context->owner[qual] = 0;
+	context->owner[qual] = NULL;
 
 	/*
 	 * we put the context twice: