Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 3656849..36d8092 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -578,7 +578,7 @@
 
 	mutex_lock(&kvm->slots_lock);
 
-	/* Verify that there isnt a match already */
+	/* Verify that there isn't a match already */
 	if (ioeventfd_check_collision(kvm, p)) {
 		ret = -EEXIST;
 		goto unlock_fail;