clk: lan966x: Remove unused round_rate hook

clk: lan966x: Remove unused round_rate hook

The lan966x driver registers a gck clock with both a determine_rate and
a round_rate implementation. Both are equivalent, and are only called by
clk_core_determine_round_nolock() which favors determine_rate.

Thus, lan966x_gck_round_rate() is never called, so we can just remove
it.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20221018-clk-range-checks-fixes-v4-5-971d5077e7d2@cerno.tech
Signed-off-by: Stephen Boyd <sboyd@kernel.org>