x86: kvm: remove NULL check before kfree

kfree can handle NULL pointer as its argument.
According to coccinelle isnullfree check, remove NULL check
before kfree operation.
Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
Message-Id: <20220614133458.147314-1-dzm91@hust.edu.cn>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kernel/kvm.c

@@ -236,7 +236,6 @@ void kvm_async_pf_task_wake(u32 token)
 	raw_spin_unlock(&b->lock);
 
 	/* A dummy token might be allocated and ultimately not used.  */
-	if (dummy)
 	kfree(dummy);
 }
 EXPORT_SYMBOL_GPL(kvm_async_pf_task_wake);