KVM: PPC: Only WARN on invalid emulation

When we hit an emulation result that we didn't expect, that is an error,
but it's nothing that warrants a BUG(), because it can be guest triggered.

So instead, let's only WARN() the user that this happened.

Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index be83fca..e2225e5 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -237,7 +237,8 @@
 		r = RESUME_HOST;
 		break;
 	default:
-		BUG();
+		WARN_ON(1);
+		r = RESUME_GUEST;
 	}
 
 	return r;