When comparing a pointer, it's clearer to compare it to NULL than to 0.

[ tglx: arch/x86 adaptation ]
Signed-off-by: NYoann Padioleau <padator@wanadoo.fr>
Signed-off-by: NAndi Kleen <ak@suse.de>
Cc: ak@suse.de
Cc: discuss@x86-64.org
Cc: akpm@linux-foundation.org
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>