m/n/k/p/kvmdevice: fix device inode error handling

This was broken in d5f851bb47, where the inverted logic was not kept
when migrating to errors.Is.

Change-Id: Id1bbc96f80b33df539a3a5051d56e126bb453390
Reviewed-on: https://review.monogon.dev/c/monogon/+/3077
Tested-by: Jenkins CI
Reviewed-by: Tim Windelschmidt <tim@monogon.tech>
diff --git a/metropolis/node/kubernetes/plugins/kvmdevice/kvmdevice.go b/metropolis/node/kubernetes/plugins/kvmdevice/kvmdevice.go
index 007bde6..90fdc44 100644
--- a/metropolis/node/kubernetes/plugins/kvmdevice/kvmdevice.go
+++ b/metropolis/node/kubernetes/plugins/kvmdevice/kvmdevice.go
@@ -163,7 +163,7 @@
 	}
 
 	err = unix.Mknod("/dev/kvm", 0660, int(kvmDevNode))
-	if err != nil && errors.Is(err, unix.EEXIST) {
+	if err != nil && !errors.Is(err, unix.EEXIST) {
 		return fmt.Errorf("failed to create KVM device node: %v", err)
 	}