scripts/atomic/check-atomics.sh: don't assume that scripts are executable

scripts/atomic/check-atomics.sh: don't assume that scripts are executable

patch(1) doesn't set the x bit on files.  So if someone downloads and
applies patch-4.21.xz, their kernel won't build.  Fix that by executing
/bin/sh.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>