locking/atomics: Check atomic-arch-fallback.h too

The sha1sum of include/linux/atomic-arch-fallback.h isn't checked by
check-atomics.sh. It's not clear why it's skipped so let's check it too.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lkml.kernel.org/r/20201001202028.1048418-1-pebolle@tiscali.nl