rust: enable `clippy::ptr_cast_constness` lint

In Rust 1.72.0, Clippy introduced the `ptr_cast_constness` lint [1]:

> Though `as` casts between raw pointers are not terrible,
> `pointer::cast_mut` and `pointer::cast_const` are safer because they
> cannot accidentally cast the pointer to another type.

There are only 3 affected sites:
- `*mut T as *const U as *mut U` becomes `(*mut T).cast()`.
- `&self as *const Self as *mut Self` becomes
  `core::ptr::from_ref(self).cast_mut()`.
- `*const T as *mut _` becommes `(*const T).cast_mut()`.

Apply these changes and enable the lint -- no functional change
intended.

Link: https://rust-lang.github.io/rust-clippy/master/index.html#ptr_cast_constness [1]
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Link: https://lore.kernel.org/r/20250615-ptr-as-ptr-v12-2-f43b024581e8@gmail.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index 25c19877b903..63b705d99631 100644
--- a/Makefile
+++ b/Makefile
@@ -485,6 +485,7 @@ export rust_common_flags := --edition=2021 \
 			    -Aclippy::needless_lifetimes \
 			    -Wclippy::no_mangle_with_rust_abi \
 			    -Wclippy::ptr_as_ptr \
+			    -Wclippy::ptr_cast_constness \
 			    -Wclippy::undocumented_unsafe_blocks \
 			    -Wclippy::unnecessary_safety_comment \
 			    -Wclippy::unnecessary_safety_doc \