ena: Make first_interrupt a uint8_t

[markj]

Summary

Avoid passing vars of type bool to atomic(9) routines. The size of bool
is not fixed by the C standard, even though it's one byte by convention.

This fixes the KASAN and KMSAN builds, which fail because the compiler
refuses to silently cast a _Bool * to a uint8_t * when calling the
atomic(9) interceptors.

Fixes: 0ac122c388d9 ("ena: Use atomic_load/store functions for first_interrupt variable")

Test Plan

build GENERIC-KASAN and GENERIC-KMSAN amd64 kernels

[dgr_semihalf.com]

LGTM