target/i386: kvm: just return after migrate_add_blocker failed

When migrate_add_blocker failed, the invtsc_mig_blocker is not
appended so no need to remove. This can save several instructions.
Signed-off-by: NLi Qiang <liq3ea@163.com>
Message-Id: <20181006091816.7659-1-liq3ea@163.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

target/i386/kvm.c

@@ -1198,7 +1198,7 @@ int kvm_arch_init_vcpu(CPUState *cs)
             if (local_err) {
                 error_report_err(local_err);
                 error_free(invtsc_mig_blocker);
-                goto fail;
+                return r;
             }
             /* for savevm */
             vmstate_x86_cpu.unmigratable = 1;