watchdog: davinci: add support for deferred probing

devm_clk_get can fail with EPROBE_DEFER in case the clock provider is
not ready yet. Handle this case gracefully, rather than dumping out
a huge warning.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>