Fix segfault in "mcelog --help"

The cpu_choices list in mcelog.c needs some kind of NULL entry at
the end to prevent the loops that iterate through all the entries
from falling off the end.  The loops look for NULL, not the size
of the array.

Signed-off-by: Andi Kleen <ak@linux.intel.com>

mcelog.c

@@ -273,6 +273,7 @@ static struct config_choice cpu_choices[] = {
 	{ "broadwell", CPU_BROADWELL },
 	{ "xeon-v2", CPU_IVY_BRIDGE_EPEX },
 	{ "xeon-v3", CPU_HASWELL_EPEX },
+	{ NULL }
 };
 
 static void print_cputypes(void)