watchdog: asm9260_wdt: fix error handling in asm9260_wdt_probe()

If devm_reset_control_get_exclusive() fails, asm9260_wdt_probe()
returns immediately. But clks has been already enabled at that point,
so it is required to disable them or to move the code around.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>