locking/atomic, arch/arc: Fix build

Resolve conflict between commits:

  fbffe892 ("locking/atomic, arch/arc: Implement atomic_fetch_{add,sub,and,andnot,or,xor}()")

and:

  ed6aefed ("Revert "ARCv2: spinlock/rwlock/atomics: Delayed retry of failed SCOND with exponential backoff"")

Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nigel Topham <ntopham@synopsys.com>
Cc: Noam Camus <noamc@ezchip.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-snps-arc@lists.infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>