drm/vc4: kms: Warn if clk_set_min_rate fails

We currently ignore the clk_set_min_rate return code assuming it would
succeed. However, it can fail if we ask for a rate higher than the
current maximum for example.

Since we can't fail in atomic_commit, at least warn on failure.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>