watchdog: Use dev_read only if OF_PLATDATA is not enabled

Currently watchdog tries to use dev_read_u32_default to get timeout
configuration in case OF_CONTROL is enabled. However, if SPL is
built with OF_PLATDATA this has no sense as there is no device tree.

This patch fixes this issue by only use dev_read_u32_default if OF_CONTROL
is enabled but OF_PLATDATA is not.

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>
Reviewed-by: Simon Glass <sjg@chromium.org>