rust: bits: always inline functions using build_assert with arguments

`build_assert` relies on the compiler to optimize out its error path.
Functions using it with its arguments must thus always be inlined,
otherwise the error path of `build_assert` might not be optimized out,
triggering a build error.

Cc: stable@vger.kernel.org
Fixes: cc84ef3 ("rust: bits: add support for bits/genmask macros")
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://patch.msgid.link/20251208-io-build-assert-v3-4-98aded02c1ea@nvidia.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: Gnurou

rust/kernel/bits.rs

@@ -27,7 +27,8 @@ macro_rules! impl_bit_fn {
             ///
             /// This version is the default and should be used if `n` is known at
             /// compile time.
-            #[inline]
+            // Always inline to optimize out error path of `build_assert`.
+            #[inline(always)]
             pub const fn [<bit_ $ty>](n: u32) -> $ty {
                 build_assert!(n < <$ty>::BITS);
                 (1 as $ty) << n
@@ -75,7 +76,8 @@ macro_rules! impl_genmask_fn {
             /// This version is the default and should be used if the range is known
             /// at compile time.
             $(#[$genmask_ex])*
-            #[inline]
+            // Always inline to optimize out error path of `build_assert`.
+            #[inline(always)]
             pub const fn [<genmask_ $ty>](range: RangeInclusive<u32>) -> $ty {
                 let start = *range.start();
                 let end = *range.end();