test: dm: clk_ccf: fix building error

Fix unused variable error produced by building tests

Fixes: d3061824 (test: dm: clk_ccf: test ccf_clk_ops)
Signed-off-by: Yang Xiwen <forbidden405@outlook.com>
Reviewed-by: Sean Anderson <seanga2@gmail.com>
Link: https://lore.kernel.org/r/20231216-b4-fix_build-v1-1-b8e79c94744f@outlook.com