genirq: Provide irq_force_affinity fallback for non-SMP

Patch 01f8fa4 "genirq: Allow forcing cpu affinity of interrupts" added
an irq_force_affinity() function, and 30ccf03 "clocksource: Exynos_mct:
Use irq_force_affinity() in cpu bringup" subsequently uses it. However, the
driver can be used with CONFIG_SMP disabled, but the function declaration
is only available for CONFIG_SMP, leading to this build error:

drivers/clocksource/exynos_mct.c:431:3: error: implicit declaration of function 'irq_force_affinity' [-Werror=implicit-function-declaration]
   irq_force_affinity(mct_irqs[MCT_L0_IRQ + cpu], cpumask_of(cpu));

This patch introduces a dummy helper function for the non-SMP case
that always returns success, to get rid of the build error.
Since the patches causing the problem are marked for stable backports,
this one should be as well.

Signed-off-by: Arnd Bergmann <[email protected]>
Cc: Krzysztof Kozlowski <[email protected]>
Acked-by: Kukjin Kim <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/5619084.0zmrrIUZLV@wuerfel
Signed-off-by: Thomas Gleixner <[email protected]>

Author: arndb

include/linux/interrupt.h

@@ -272,6 +272,11 @@ static inline int irq_set_affinity(unsigned int irq, const struct cpumask *m)
 	return -EINVAL;
 }
 
+static inline int irq_force_affinity(unsigned int irq, const struct cpumask *cpumask)
+{
+	return 0;
+}
+
 static inline int irq_can_set_affinity(unsigned int irq)
 {
 	return 0;