mce->socketid and cpu_data(mce->cpu).phys_proc_id are the same,
compare with mce_setup (in mce.c):
	m->cpu = m->extcpu = smp_processor_id();
        ...
	m->socketid = cpu_data(m->extcpu).phys_proc_id;

This makes it easier for example for XEN patches to hook into
the MCE subsystem.
Compile tested on x86_64.
Signed-off-by: Thomas Renninger <trenn@suse.de>
CC: JBeulich@novell.com
CC: linux-edac@vger.kernel.org
CC: Mauro Carvalho Chehab <mchehab@redhat.com>