rtc: hym8563: fix incorrect maximum clock rate handling

When hym8563_clkout_round_rate() is called with a requested rate higher
than the highest supported rate, it currently returns 0, which disables
the clock. According to the clk API, round_rate() should instead return
the highest supported rate. Update the function to return the maximum
supported rate in this case.

Fixes: dcaf0384 ("rtc: add hym8563 rtc-driver")
Signed-off-by: Brian Masney <bmasney@redhat.com>
Link: https://lore.kernel.org/r/20250710-rtc-clk-round-rate-v1-2-33140bb2278e@redhat.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>