Use #!cfg_attr for inline_asm
This fixes the previous commit where the #![feature()]
flag was used by mistake.
-#![feature(llvm_asm)]
//! Low level access to Cortex-M processors
//!
//! This crate provides:
//! This crate is guaranteed to compile on stable Rust 1.31 and up. It *might*
//! compile with older versions but that may change in any new patch release.
-#![cfg_attr(feature = "inline-asm", feature(asm))]
+#![cfg_attr(feature = "inline-asm", feature(llvm_asm))]
#![deny(missing_docs)]
#![no_std]
#![allow(clippy::identity_op)]
