Sync with latest cortex-m version

[sbechet]

It's not really a bug, but I can't do this synchronization. There is currently something that I did not understand in the functioning of rust

I tried to replace init() with:

use core::borrow::BorrowMut;
use core::ops::DerefMut;
use cortex_m::interrupt::Mutex;
use linked_list_allocator::Heap;
// ...
pub struct CortexMHeap {
    heap: Mutex<Heap>,
}
// ...

    pub unsafe fn init(&self, start_addr: usize, size: usize) {
        cortex_m::interrupt::free(|cs| {
               self.heap
                    .borrow(cs)
                    .borrow_mut()
                    .deref_mut()
                    .init(start_addr, size);
            });
    }
}

but answer is:

error[E0596]: cannot borrow data in a `&` reference as mutable
   --> src/lib.rs:103:17
    |
103 | /                 self.heap
104 | |                     .borrow(cs)
105 | |                     .borrow_mut()
106 | |                     .deref_mut()
    | |________________________________^ cannot borrow as mutable