watchdog: always print when registering watchdog fails

So far, only 'watchdog_register_device' prints an error if registering
the watchdog driver fails. '__watchdog_register_device' doesn't.
Refactor the code so that both print out. Drivers can then rely on that
and skip their own error messages.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20241004200314.5459-2-wsa+renesas@sang-engineering.com


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