target-i386: Fix x86_cpuid_set_model_id()

Don't assume zeroed cpuid_model[] fields.

This didn't break anything yet but QOM properties should be able to set
the value to something else without setting an intermediate zero string.
Signed-off-by: NAndreas Färber <afaerber@suse.de>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

target-i386/cpu.c

@@ -627,6 +627,7 @@ static void x86_cpuid_set_model_id(CPUX86State *env, const char *model_id)
         model_id = "";
     }
     len = strlen(model_id);
+    memset(env->cpuid_model, 0, 48);
     for (i = 0; i < 48; i++) {
         if (i >= len) {
             c = '\0';