Replace pr_warn!() with pr_warn_once!() in module_param::set_param() to
avoid flooding the kernel log when a null pointer is repeatedly passed.

The original code had a TODO comment noting that pr_warn_once should be
used once available. Since pr_warn_once!() is now available, switch to it
and update the comment accordingly.

Signed-off-by: Xiaobo Liu <cppcoffee@gmail.com>
---
 rust/kernel/module_param.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/module_param.rs b/rust/kernel/module_param.rs
index 6a8a7a875..fedb709fa 100644
--- a/rust/kernel/module_param.rs
+++ b/rust/kernel/module_param.rs
@@ -62,8 +62,8 @@ pub trait ModuleParam: Sized + Copy {
     // NOTE: If we start supporting arguments without values, val _is_ allowed
     // to be null here.
     if val.is_null() {
-        // TODO: Use pr_warn_once available.
-        crate::pr_warn!("Null pointer passed to `module_param::set_param`");
+        // `pr_warn_once` is already available, use it.
+        crate::pr_warn_once!("Null pointer passed to `module_param::set_param`");
         return EINVAL.to_errno();
     }
 
-- 
2.34.1