qtest/npcm7xx_pwm-test: Fix memleak in pwm_qom_get

The pwm_qom_get function didn't free "response", which caused an indirect
memory leak. So use qobject_unref() to fix it.

ASAN shows memory leak stack:

Indirect leak of 74160000 byte(s) in 18000 object(s) allocated from:
    #0 0x7f96e2f79d4e in __interceptor_calloc (/lib64/libasan.so.5+0x112d4e)
    #1 0x7f96e2d98a50 in g_malloc0 (/lib64/libglib-2.0.so.0+0x55a50)
    qemu#2 0x556313112180 in qdict_new ../qobject/qdict.c:30
    qemu#3 0x556313115bca in parse_object ../qobject/json-parser.c:318
    qemu#4 0x556313117810 in parse_value ../qobject/json-parser.c:546
    qemu#5 0x556313117bda in json_parser_parse ../qobject/json-parser.c:580
    qemu#6 0x55631310fe67 in json_message_process_token ../qobject/json-streamer.c:92
    qemu#7 0x5563131210b7 in json_lexer_feed_char ../qobject/json-lexer.c:313
    qemu#8 0x556313121662 in json_lexer_feed ../qobject/json-lexer.c:350
    qemu#9 0x5563131101e9 in json_message_parser_feed ../qobject/json-streamer.c:121
    qemu#10 0x5563130cb81e in qmp_fd_receive ../tests/qtest/libqtest.c:614
    qemu#11 0x5563130cba2b in qtest_qmp_receive_dict ../tests/qtest/libqtest.c:636
    qemu#12 0x5563130cb939 in qtest_qmp_receive ../tests/qtest/libqtest.c:624
    qemu#13 0x5563130cbe0d in qtest_vqmp ../tests/qtest/libqtest.c:715
    qemu#14 0x5563130cc40f in qtest_qmp ../tests/qtest/libqtest.c:756
    qemu#15 0x5563130c5623 in pwm_qom_get ../tests/qtest/npcm7xx_pwm-test.c:180
    qemu#16 0x5563130c595e in pwm_get_duty ../tests/qtest/npcm7xx_pwm-test.c:210
    qemu#17 0x5563130c7529 in test_toggle ../tests/qtest/npcm7xx_pwm-test.c:447

Reported-by: Euler Robot <euler.robot@huawei.com>
Message-Id: <20210115075634.717909-1-ganqixin@huawei.com>
Signed-off-by: Gan Qixin <ganqixin@huawei.com>
Reviewed-by: Havard Skinnemoen <hskinnemoen@google.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Hao Wu <wuhaotsh@google.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

Author: Ganqx

tests/qtest/npcm7xx_pwm-test.c

@@ -175,14 +175,17 @@ static int pwm_index(const PWM *pwm)
 static uint64_t pwm_qom_get(QTestState *qts, const char *path, const char *name)
 {
     QDict *response;
+    uint64_t val;
 
     g_test_message("Getting properties %s from %s", name, path);
     response = qtest_qmp(qts, "{ 'execute': 'qom-get',"
             " 'arguments': { 'path': %s, 'property': %s}}",
             path, name);
     /* The qom set message returns successfully. */
     g_assert_true(qdict_haskey(response, "return"));
-    return qnum_get_uint(qobject_to(QNum, qdict_get(response, "return")));
+    val = qnum_get_uint(qobject_to(QNum, qdict_get(response, "return")));
+    qobject_unref(response);
+    return val;
 }
 
 static uint64_t pwm_get_freq(QTestState *qts, int module_index, int pwm_index)