Fix memory leaks in drm/tests with drm_kunit_display_mode_from_cea_vic()

Summary

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.