clk: zynqmp: divider: convert from divider_round_rate() to divider_determine_rate()

clk: zynqmp: divider: convert from divider_round_rate() to divider_determine_rate()

The divider_round_rate() function is now deprecated, so let's migrate
to divider_determine_rate() instead so that this deprecated API can be
removed.

Note that when the main function itself was migrated to use
determine_rate, this was mistakenly converted to:

    req->rate = divider_round_rate(...)

This is invalid in the case when an error occurs since it can set the
rate to a negative value.

Fixes: 0f9cf96a01fd ("clk: zynqmp: divider: convert from round_rate() to determine_rate()")
Signed-off-by: Brian Masney <bmasney@redhat.com>