alloc: Yield on a panic

If we panic we need ot yield to ensure any remaining prints are printed
by the kernel. This helps with debugging.

We use future::pending() instead of syscalls::raw::yieldk() to reduce
the amount of unsafe code.

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

src/alloc.rs

diff --git a/src/alloc.rs b/src/alloc.rs
index ee3de18..523cb64 100644
--- a/src/alloc.rs
+++ b/src/alloc.rs
@@ -8,6 +8,7 @@
 use core::executor;
 use core::ptr;
 use core::ptr::NonNull;
+use futures::future;
 use linked_list_allocator::Heap;
 
 pub static mut HEAP: Heap = Heap::empty();
@@ -40,6 +41,8 @@
 
         if let (Ok(leds_driver), Ok(timer_driver)) = (leds_driver, timer_driver) {
             let _ = cycle_all_leds(&leds_driver, &timer_driver).await;
+        } else {
+            future::pending::<()>().await
         }
         loop {}
     })