ppc/e500: Free irqs array to avoid memleak

When running qom-test, a memory leak occurred in the ppce500_init function,
this patch free irqs array to fix it.

ASAN shows memory leak stack:

Direct leak of 40 byte(s) in 1 object(s) allocated from:
    #0 0xfffc5ceee1f0 in __interceptor_calloc (/lib64/libasan.so.5+0xee1f0)
    #1 0xfffc5c806800 in g_malloc0 (/lib64/libglib-2.0.so.0+0x56800)
    #2 0xaaacf9999244 in ppce500_init qemu/hw/ppc/e500.c:859
    qemu#3 0xaaacf97434e8 in machine_run_board_init qemu/hw/core/machine.c:1134
    qemu#4 0xaaacf9c9475c in qemu_init qemu/softmmu/vl.c:4369
    qemu#5 0xaaacf94785a0 in main qemu/softmmu/main.c:49

Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Gan Qixin <ganqixin@huawei.com>
Message-Id: <20201204075822.359832-1-ganqixin@huawei.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

hw/ppc/e500.c

@@ -926,6 +926,7 @@ void ppce500_init(MachineState *machine)
                                 ccsr_addr_space);
 
     mpicdev = ppce500_init_mpic(pms, ccsr_addr_space, irqs);
+    g_free(irqs);
 
     /* Serial */
     if (serial_hd(0)) {