RISC-V: KVM: Simplify kvm_arch_prepare_memory_region()

In kvm_arch_prepare_memory_region(), if no error occurs, a spin_lock()/
spin_unlock() call can be avoided.

Switch to kvm_riscv_gstage_iounmap() that is the same as the current code,
but with a better semantic.
It also embeds the locking logic. So it is avoided if ret == 0.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Anup Patel <anup@brainfault.org>

arch/riscv/kvm/mmu.c

@@ -537,10 +537,8 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	if (change == KVM_MR_FLAGS_ONLY)
 		goto out;
 
-	spin_lock(&kvm->mmu_lock);
 	if (ret)
-		gstage_unmap_range(kvm, base_gpa, size, false);
-	spin_unlock(&kvm->mmu_lock);
+		kvm_riscv_gstage_iounmap(kvm, base_gpa, size);
 
 out:
 	mmap_read_unlock(current->mm);