mips: fix obsolete cpumask_of_cpu usage.

Plus, it's weird.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

arch/mips/include/asm/smp.h

@@ -88,7 +88,7 @@ static inline void arch_send_call_function_single_ipi(int cpu)
 {
 	extern struct plat_smp_ops *mp_ops;	/* private */
 
-	mp_ops->send_ipi_mask(&cpumask_of_cpu(cpu), SMP_CALL_FUNCTION);
+	mp_ops->send_ipi_mask(cpumask_of(cpu), SMP_CALL_FUNCTION);
 }
 
 static inline void arch_send_call_function_ipi_mask(const struct cpumask *mask)