irqdomain: Fix a memory leak in irq_domain_push_irq()

Fix a memory leak reported by kmemleak:
unreferenced object 0xffff000bc6f50e80 (size 128):
  comm "kworker/23:2", pid 201, jiffies 4294894947 (age 942.132s)
  hex dump (first 32 bytes):
    00 00 00 00 41 00 00 00 86 c0 03 00 00 00 00 00  ....A...........
    00 a0 b2 c6 0b 00 ff ff 40 51 fd 10 00 80 ff ff  ........@Q......
  backtrace:
    [<00000000e62d2240>] kmem_cache_alloc_trace+0x1a4/0x320
    [<00000000279143c9>] irq_domain_push_irq+0x7c/0x188
    [<00000000d9f4c154>] thunderx_gpio_probe+0x3ac/0x438
    [<00000000fd09ec22>] pci_device_probe+0xe4/0x198
    [<00000000d43eca75>] really_probe+0xdc/0x320
    [<00000000d3ebab09>] driver_probe_device+0x5c/0xf0
    [<000000005b3ecaa0>] __device_attach_driver+0x88/0xc0
    [<000000004e5915f5>] bus_for_each_drv+0x7c/0xc8
    [<0000000079d4db41>] __device_attach+0xe4/0x140
    [<00000000883bbda9>] device_initial_probe+0x18/0x20
    [<000000003be59ef6>] bus_probe_device+0x98/0xa0
    [<0000000039b03d3f>] deferred_probe_work_func+0x74/0xa8
    [<00000000870934ce>] process_one_work+0x1c8/0x470
    [<00000000e3cce570>] worker_thread+0x1f8/0x428
    [<000000005d64975e>] kthread+0xfc/0x128
    [<00000000f0eaa764>] ret_from_fork+0x10/0x18

Fixes: 495c38d3 ("irqdomain: Add irq_domain_{push,pop}_irq() functions")
Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20200120043547.22271-1-haokexin@gmail.com