selftest: media_tests: fix trivial UAF typo

Stumbled upon this typo while looking for something else.

Link: https://lore.kernel.org/lkml/20241205194829.3449669-1-cmllamas@google.com/


Cc: Shuah Khan <shuah@kernel.org>
Fixes: fe8777a8 ("selftests: add media controller regression test scripts and document")
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>