watchdog: dw_wdt: Simplify clk management

Use devm_clk_get_enabled() instead of hand-writing it.
This saves some LoC.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/f6094c55cacf9637d835cd49290d9e888faeb0f7.1682491863.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>