MIPS: smp-cps: Convert smp_mb__after_atomic_dec()

Commit 91bbefe6 "arch,mips: Convert smp_mb__*()" replaced the
smp_mb__after_atomic_dec function with smp_mb__after_atomic, whilst
commit 1d8f1f5a "MIPS: smp-cps: hotplug support" introduced a new
use of it. Replace that use with smp_mb__after_atomic in order to avoid
a build failure:

  arch/mips/kernel/smp-cps.c: In function 'cps_cpu_disable':
  arch/mips/kernel/smp-cps.c:304:2: error: 'smp_mb__after_atomic_dec' is
    deprecated (declared at include/linux/atomic.h:35)
    [-Werror=deprecated-declarations]
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Reviewed-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7085/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/smp-cps.c

@@ -301,7 +301,7 @@ static int cps_cpu_disable(void)
 
 	core_cfg = &mips_cps_core_bootcfg[current_cpu_data.core];
 	atomic_sub(1 << cpu_vpe_id(&current_cpu_data), &core_cfg->vpe_mask);
-	smp_mb__after_atomic_dec();
+	smp_mb__after_atomic();
 	set_cpu_online(cpu, false);
 	cpu_clear(cpu, cpu_callin_map);