kernel: Replace kmalloc() usages with kzalloc() (#2939)

This ensures we won't use uninitialized pointers for task work.

kernel/kernel_umount.c

@@ -156,7 +156,7 @@ int ksu_handle_umount(uid_t old_uid, uid_t new_uid)
     // umount the target mnt
     pr_info("handle umount for uid: %d, pid: %d\n", new_uid, current->pid);
 
-    tw = kmalloc(sizeof(*tw), GFP_ATOMIC);
+    tw = kzalloc(sizeof(*tw), GFP_ATOMIC);
     if (!tw)
         return 0;