clk: mediatek: remove unused array audio_parents

Array audio_parents is declared but never used, hence it is redundant
and can be removed.

Cleans up clang warning:
warning: 'audio_parents' defined but not used [-Wunused-const-variable=]

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>