SCB.ICSR is more than 8 bits

[Dirbaio]

This code here reads ICSR and casts it to 8 bits. In cortex-m3 it is more than 8 bits because there can be up to 480 interrupts.

cortex-m-rt/macros/src/lib.rs

Line 230 in ca4790f

let irqn = unsafe { core::ptr::read(SCB_ICSR) as u8 as i16 - 16 };

This is the same as rust-embedded/cortex-m#332

[adamgreig]

Closed by #315.