x86, ptrace: PEBS support, warning fix

arch/x86/kernel/process_32.c:566: warning: unused variable 'ds_next'
arch/x86/kernel/process_32.c:566: warning: unused variable 'ds_prev'

Cc: Markus Metzger <markus.t.metzger@intel.com>
Cc: Andi Kleen <ak@suse.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Michael Kerrisk <mtk.manpages@googlemail.com>
Cc: <juan.villacis@intel.com>
Cc: stephane eranian <eranian@googlemail.com>
Cc: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>