rtc: pcf8563: fix incorrect maximum clock rate handling

[ Upstream commit 906726a5efeefe0ef0103ccff5312a09080c04ae ]

When pcf8563_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: a39a6405 ("rtc: pcf8563: add CLKOUT to common clock framework")
Signed-off-by: Brian Masney <bmasney@redhat.com>
Link: https://lore.kernel.org/r/20250710-rtc-clk-round-rate-v1-5-33140bb2278e@redhat.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>