x86: fix bootup crash in native_read_tsc()

fix bootup crash in native_read_tsc() that was reported on an Athlon-XP
and bisected. The correct feature boundary for X86_FEATURE_MFENCE_RDTSC
is not XMM but XMM2.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Acked-by: NH. Peter Anvin <hpa@zytor.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/x86/kernel/cpu/amd.c

@@ -304,7 +304,7 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c)
 	if (c->x86 < 6)
 		clear_bit(X86_FEATURE_MCE, c->x86_capability);
 
-	if (cpu_has_xmm)
+	if (cpu_has_xmm2)
 		set_bit(X86_FEATURE_MFENCE_RDTSC, c->x86_capability);
 }