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.

Reviewed-by: Eduardo Habhost <ehabkost@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
[AF: Use memset() instead of for loop, suggested by Igor]
Signed-off-by: Andreas Färber <afaerber@suse.de>

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';