drm/panic: clean new clippy::needless_range_loop lint for Rust 1.100.0

Starting with Rust 1.100.0 (expected 2026-11-12), Clippy warns:

    warning: the loop variable `i` is only used to index `self.decimals`
       --> drivers/gpu/drm/drm_panic_qr.rs:410:18
        |
    410 |         for i in 0..len {
        |                  ^^^^^^
        |
    note: for this index operation
       --> drivers/gpu/drm/drm_panic_qr.rs:411:13
        |
    411 |             self.decimals[i] = (chunk % 10) as u8;
        |             ^^^^^^^^^^^^^^^^
        = help: for further information visit https://rust-lang.github.io/rust-clippy/main/index.html#needless_range_loop
        = note: `-W clippy::needless-range-loop` implied by `-W clippy::all`
        = help: to override `-W clippy::all` add `#[allow(clippy::needless_range_loop)]`
    help: consider using an iterator
        |
    410 -         for i in 0..len {
    410 +         for <item> in self.decimals.iter_mut().take(len) {
        |

The lint did not trigger here before because it could not handle arrays
behind a field access such as `self.decimals` -- Clippy was improved to
catch those cases [1][2].

Thus clean the warning by iterating over a slice rather than using
`take()` so that an out-of-range `len` still triggers the same bounds
check as the indexed loop.

Cc: stable@vger.kernel.org # Needed in 6.18.y and later.
Link: https://github.com/rust-lang/rust-clippy/issues/16631 [1]
Link: https://github.com/rust-lang/rust-clippy/pull/16634 [2]
Assisted-by: LLM
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patch.msgid.link/20260826145642.43807-1-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

drivers/gpu/drm/drm_panic_qr.rs

@@ -407,8 +407,8 @@ fn push(&mut self, data: u64, len: usize) {
         for i in (0..self.len).rev() {
             self.decimals[i + len] = self.decimals[i];
         }
-        for i in 0..len {
-            self.decimals[i] = (chunk % 10) as u8;
+        for decimal in &mut self.decimals[..len] {
+            *decimal = (chunk % 10) as u8;
             chunk = div10(chunk);
         }
         self.len += len;