watchdog: marvell_gti_wdt: Fix error code in probe()

This error path accidentally returns success.  Return -EINVAL instead.

Fixes: ef9e7fe2 ("Watchdog: Add marvell GTI watchdog driver")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Bharat Bhushan <bbhushan2@marvell.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/af326fd7-ac71-43a1-b7de-81779b61d242@moroto.mountain


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