watchdog: airoha: Prevent division by zero when clock frequency is zero

watchdog: airoha: Prevent division by zero when clock frequency is zero

clk_get_rate() can return 0 when the clock provider is not properly
configured or the clock is unmanaged. The driver uses wdt_freq as a
divisor directly in airoha_wdt_probe() to compute max_timeout and in
airoha_wdt_get_timeleft() to compute the remaining time, which results
in a division by zero.

Add a check for wdt_freq == 0 in probe and return -EINVAL with
dev_err_probe() to prevent the division by zero and provide a
diagnostic message.

Fixes: 3cf67f3769b8 ("watchdog: Add support for Airoha EN7851 watchdog")
Signed-off-by: Wayen Yan <win847@gmail.com>
Link: https://lore.kernel.org/r/178347932594.81327.4834644880399144119@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>