clk: sophgo: sg2042-pll: remove round_rate() in favor of determine_rate()

This driver implements both the determine_rate() and round_rate() clk
ops, and the round_rate() clk ops is deprecated. When both are defined,
clk_core_determine_round_nolock() from the clk core will only use the
determine_rate() clk ops, so let's remove the round_rate() clk ops since
it's unused.

The implementation of sg2042_clk_pll_determine_rate() calls
sg2042_clk_pll_round_rate(), so this folds the two into a single
function.

Reviewed-by: Chen Wang <unicorn_wang@outlook.com>
Tested-by: Chen Wang <unicorn_wang@outlook.com> # Pioneerbox
Signed-off-by: Brian Masney <bmasney@redhat.com>