rust: macros: indent list item in `module!`'s docs

Like commit e516211f615f ("rust: macros: indent list item in `paste!`'s
docs"), but for `module!`.

Reviewed-by: Trevor Gross <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Miguel Ojeda <[e-mail]>

rust/macros/lib.rs

···
 ///   - `license`: ASCII string literal of the license of the kernel module (required).
 ///   - `alias`: array of ASCII string literals of the alias names of the kernel module.
 ///   - `firmware`: array of ASCII string literals of the firmware files of
-/// the kernel module.
+///     the kernel module.
 #[proc_macro]
 pub fn module(ts: TokenStream) -> TokenStream {
     module::module(ts)