rust: bitmap: clean Rust 1.92.0 unused_unsafe warning

Starting with Rust 1.92.0 (expected 2025-12-11), Rust allows to safely
take the address of a union field [1][2]:

      CLIPPY L rust/kernel.o
    error: unnecessary `unsafe` block
       --> rust/kernel/bitmap.rs:169:13
        |
    169 |             unsafe { core::ptr::addr_of!(self.repr.bitmap) }
        |             ^^^^^^ unnecessary `unsafe` block
        |
        = note: `-D unused-unsafe` implied by `-D warnings`
        = help: to override `-D warnings` add `#[allow(unused_unsafe)]`

    error: unnecessary `unsafe` block
       --> rust/kernel/bitmap.rs:185:13
        |
    185 |             unsafe { core::ptr::addr_of_mut!(self.repr.bitmap) }
        |             ^^^^^^ unnecessary `unsafe` block

Thus allow both instances to clean the warning in newer compilers.

Link: rust-lang/rust#141264 [1]
Link: rust-lang/rust#141469 [2]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>

Author: ojeda

rust/kernel/bitmap.rs

@@ -166,6 +166,7 @@ impl core::ops::Deref for BitmapVec {
     fn deref(&self) -> &Bitmap {
         let ptr = if self.nbits <= BITS_PER_LONG {
             // SAFETY: Bitmap is represented inline.
+            #[allow(unused_unsafe, reason = "Safe since Rust 1.92.0")]
             unsafe { core::ptr::addr_of!(self.repr.bitmap) }
         } else {
             // SAFETY: Bitmap is represented as array of `unsigned long`.
@@ -182,6 +183,7 @@ impl core::ops::DerefMut for BitmapVec {
     fn deref_mut(&mut self) -> &mut Bitmap {
         let ptr = if self.nbits <= BITS_PER_LONG {
             // SAFETY: Bitmap is represented inline.
+            #[allow(unused_unsafe, reason = "Safe since Rust 1.92.0")]
             unsafe { core::ptr::addr_of_mut!(self.repr.bitmap) }
         } else {
             // SAFETY: Bitmap is represented as array of `unsigned long`.