rust_out_of_tree: use string literals in `module!` macro

See commit 593e65924b2e ("rust: take str literal instead bstr literal
in `module!` macro") in the main repository:

    For simplicity (avoid parsing), escape sequences and raw string literals
    are not yet handled.

    Module names, aliases and license strings are restricted to ASCII only.

    Signed-off-by: Gary Guo <gary@garyguo.net>

Link: https://github.com/Rust-for-Linux/linux/issues/252
Link: https://lore.kernel.org/lkml/YukvvPOOu8uZl7+n@yadro.com/
Link: 593e65924b
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

rust_out_of_tree.rs

@@ -6,10 +6,10 @@ use kernel::prelude::*;
 
 module! {
     type: RustOutOfTree,
-    name: b"rust_out_of_tree",
-    author: b"Rust for Linux Contributors",
-    description: b"Rust out-of-tree sample",
-    license: b"GPL",
+    name: "rust_out_of_tree",
+    author: "Rust for Linux Contributors",
+    description: "Rust out-of-tree sample",
+    license: "GPL",
 }
 
 struct RustOutOfTree {