locking/atomics: Use sed(1) instead of non-standard head(1) option

POSIX says the -n option must be a positive decimal integer. Not all
implementations of head(1) support negative numbers meaning offset from
the end of the file.

Instead, the sed expression '$d' has the same effect of removing the
last line of the file.

Signed-off-by: Michael Forney <mforney@mforney.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190618053306.730-1-mforney@mforney.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>