drm/tests: hdmi: Fix memory leaks in drm_display_mode_from_cea_vic()

modprobe drm_hdmi_state_helper_test and then rmmod it, the following
memory leak occurs.

The `mode` allocated in drm_mode_duplicate() called by
drm_display_mode_from_cea_vic() is not freed, which cause the memory leak:

unreferenced object 0xffffff80ccd18100 (size 128):
comm "kunit_try_catch", pid 1851, jiffies 4295059695
hex dump (first 32 bytes):
57 62 00 00 80 02 90 02 f0 02 20 03 00 00 e0 01 Wb........ .....
ea 01 ec 01 0d 02 00 00 0a 00 00 00 00 00 00 00 ................
backtrace (crc c2f1aa95):
[<000000000f10b11b>] kmemleak_alloc+0x34/0x40
[<000000001cd4cf73>] __kmalloc_cache_noprof+0x26c/0x2f4
[<00000000f1f3cffa>] drm_mode_duplicate+0x44/0x19c
[<000000008cbeef13>] drm_display_mode_from_cea_vic+0x88/0x98
[<0000000019daaacf>] 0xffffffedc11ae69c
[<000000000aad0f85>] kunit_try_run_case+0x13c/0x3ac
[<00000000a9210bac>] kunit_generic_run_threadfn_adapter+0x80/0xec
[<000000000a0b2e9e>] kthread+0x2e8/0x374
[<00000000bd668858>] ret_from_fork+0x10/0x20
......

Free `mode` by using drm_kunit_display_mode_from_cea_vic()
to fix it.

Cc: [e-mail]
Fixes: 4af70f19e559 ("drm/tests: Add RGB Quantization tests")
Acked-by: Maxime Ripard <[e-mail]>
Signed-off-by: Jinjie Ruan <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
Signed-off-by: Maxime Ripard <[e-mail]>

drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c

···
 	ctx = drm_kunit_helper_acquire_ctx_alloc(test);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ctx);
 
-	mode = drm_display_mode_from_cea_vic(drm, 1);
+	mode = drm_kunit_display_mode_from_cea_vic(test, drm, 1);
 	KUNIT_ASSERT_NOT_NULL(test, mode);
 
 	drm = &priv->drm;
···
 	ctx = drm_kunit_helper_acquire_ctx_alloc(test);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ctx);
 
-	mode = drm_display_mode_from_cea_vic(drm, 1);
+	mode = drm_kunit_display_mode_from_cea_vic(test, drm, 1);
 	KUNIT_ASSERT_NOT_NULL(test, mode);
 
 	drm = &priv->drm;
···
 	ctx = drm_kunit_helper_acquire_ctx_alloc(test);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ctx);
 
-	mode = drm_display_mode_from_cea_vic(drm, 1);
+	mode = drm_kunit_display_mode_from_cea_vic(test, drm, 1);
 	KUNIT_ASSERT_NOT_NULL(test, mode);
 
 	drm = &priv->drm;
···
 	ctx = drm_kunit_helper_acquire_ctx_alloc(test);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ctx);
 
-	mode = drm_display_mode_from_cea_vic(drm, 1);
+	mode = drm_kunit_display_mode_from_cea_vic(test, drm, 1);
 	KUNIT_ASSERT_NOT_NULL(test, mode);
 
 	/*