genirq: Initialize request_mutex if CONFIG_SPARSE_IRQ=n

When CONFIG_SPARSE_IRQ is disable, the request_mutex in struct irq_desc
is not initialized which causes malfunction.

Fixes: 9114014cf4 ("genirq: Add mutex to irq desc to serialize request/free_irq()")
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: <linux-arm-kernel@lists.infradead.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20190404074512.145533-1-wangkefeng.wang@huawei.com

kernel/irq/irqdesc.c

@@ -558,6 +558,7 @@ int __init early_irq_init(void)
 		alloc_masks(&desc[i], node);
 		raw_spin_lock_init(&desc[i].lock);
 		lockdep_set_class(&desc[i].lock, &irq_desc_lock_class);
+		mutex_init(&desc[i].request_mutex);
 		desc_set_defaults(i, &desc[i], node, NULL, NULL);
 	}
 	return arch_early_irq_init();