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

In the Linux kernel, the following vulnerability has been resolved:

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.