MIPS: Fix up obsolete cpu_set usage

cpu_set was removed (along with a bunch of cpumask helpers) by
commit 2f0f267ea072 ("cpumask: remove deprecated functions.").

Fix this by replacing cpu_set with cpumask_set_cpu. Without this
fix the following error is triggered when CONFIG_MIPS_MT_FPAFF=y.

  arch/mips/kernel/smp-cps.c: In function 'cps_smp_setup':
  arch/mips/kernel/smp-cps.c:95:3: error: implicit declaration of function 'cpu_set' [-Werror=implicit-function-declaration]

Fixes: 90db024f140d ("MIPS: smp-cps: cpu_set FPU mask if FPU present")
Signed-off-by: Ezequiel Garcia <ezequiel.garcia@imgtec.com>
Acked-by: Niklas Cassel <niklass@axis.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9912/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/smp-cps.c

@@ -92,7 +92,7 @@ static void __init cps_smp_setup(void)
 #ifdef CONFIG_MIPS_MT_FPAFF
 	/* If we have an FPU, enroll ourselves in the FPU-full mask */
 	if (cpu_has_fpu)
-		cpu_set(0, mt_fpu_cpumask);
+		cpumask_set_cpu(0, &mt_fpu_cpumask);
 #endif /* CONFIG_MIPS_MT_FPAFF */
 }