rust: uaccess: mark UserSliceWriter method inline

When you build the kernel using the llvm-19.1.4-rust-1.83.0-x86_64
toolchain provided by kernel.org with ARCH=x86_64, the following symbol
is generated:

$nm vmlinux | grep ' _R' | rustfilt | rg UserSliceWriter
ffffffff817c3390 T <kernel::uaccess::UserSliceWriter>::write_slice

However, this Rust symbol is a trivial wrapper around the function
copy_from_user. It doesn't make sense to go through a trivial wrapper
for this function, so mark it inline.

After applying this patch, the above command will produce no output.

Suggested-by: Alice Ryhl <aliceryhl@google.com>
Link: Rust-for-Linux#1145
Signed-off-by: Antonio Hickey <contact@antoniohickey.com>

Author: antonio-hickey

rust/kernel/uaccess.rs

@@ -322,6 +322,7 @@ impl UserSliceWriter {
     /// Fails with [`EFAULT`] if the write happens on a bad address, or if the write goes out of
     /// bounds of this [`UserSliceWriter`]. This call may modify the associated userspace slice even
     /// if it returns an error.
+    #[inline]
     pub fn write_slice(&mut self, data: &[u8]) -> Result {
         let len = data.len();
         let data_ptr = data.as_ptr().cast::<c_void>();