boot-order-test: fix memleaks in boot-order-test

boot-order-test: fix memleaks in boot-order-test

It's not a big deal, but 'check qtest-ppc/ppc64' runs fail if sanitizers is enabled.
The memory leak stack is as follow:

Direct leak of 128 byte(s) in 4 object(s) allocated from:
    #0 0x7f11756f5970 in __interceptor_calloc (/lib64/libasan.so.5+0xef970)
    #1 0x7f1174f2549d in g_malloc0 (/lib64/libglib-2.0.so.0+0x5249d)
    #2 0x556af05aa7da in mm_fw_cfg_init /mnt/sdb/qemu/tests/libqos/fw_cfg.c:119
    #3 0x556af059f4f5 in read_boot_order_pmac /mnt/sdb/qemu/tests/boot-order-test.c:137
    #4 0x556af059efe2 in test_a_boot_order /mnt/sdb/qemu/tests/boot-order-test.c:47
    #5 0x556af059f2c0 in test_boot_orders /mnt/sdb/qemu/tests/boot-order-test.c:59
    #6 0x556af059f52d in test_pmac_oldworld_boot_order /mnt/sdb/qemu/tests/boot-order-test.c:152
    #7 0x7f1174f46cb9  (/lib64/libglib-2.0.so.0+0x73cb9)
    #8 0x7f1174f46b73  (/lib64/libglib-2.0.so.0+0x73b73)
    #9 0x7f1174f46b73  (/lib64/libglib-2.0.so.0+0x73b73)
    #10 0x7f1174f46f71 in g_test_run_suite (/lib64/libglib-2.0.so.0+0x73f71)
    #11 0x7f1174f46f94 in g_test_run (/lib64/libglib-2.0.so.0+0x73f94)

Reported-by: Euler Robot <[email protected]>
Signed-off-by: Pan Nengyuan <[email protected]>
Message-Id: <20200203025935[email protected]>
Reviewed-by: Thomas Huth <[email protected]>
Signed-off-by: Thomas Huth <[email protected]>