KVM-async_pf: Delete an unnecessary check before the function call "kmem_cache_destroy"

The kmem_cache_destroy() function tests whether its argument is NULL
and then returns immediately. Thus the test around the call is not needed.

This issue was detected by using the Coccinelle software.
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

virt/kvm/async_pf.c

@@ -57,8 +57,7 @@ int kvm_async_pf_init(void)
 
 void kvm_async_pf_deinit(void)
 {
-	if (async_pf_cache)
-		kmem_cache_destroy(async_pf_cache);
+	kmem_cache_destroy(async_pf_cache);
 	async_pf_cache = NULL;
 }