watchdog: sa11x0/pxa: get rid of get_clock_tick_rate

The OS timer rate used for the watchdog can now be fetched from the
standard clock API. This will remove the last user of
get_clock_tick_rate() in both pxa and sa11x0 architectures.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Russell King <rmk+kernel@armlinux.org.uk>
Acked-by: Wim Van Sebroeck <wim@iguana.be>