x86: Fix user return notifier put_cpu_var() invocation

Today's linux-next build (x86_64 allmodconfig) failed like this:

  kernel/user-return-notifier.c: In function
  'fire_user_return_notifiers': kernel/user-return-notifier.c:45:
  error: expected expression before ')' token

Introduced by commit 7c68af6e
("core, x86: Add user return notifiers") from the tip and kvm trees
but revealed by commit e0fdb0e0


("percpu: add __percpu for sparse") from the percpu tree.

Before that percpu tree commit, "put_cpu_var()" would compile
without error (even though it really needs a parameter).

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Avi Kivity <avi@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Christoph Lameter <cl@linux-foundation.org>
LKML-Reference: <20091102161722.eea4358d.sfr@canb.auug.org.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>