watchdog: sp5100_tco: Clean up sp5100_tco_setupdevice

There are too many unnecessary goto statements in sp5100_tco_setupdevice().
Rearrange the code and limit goto statements to error handling.

Cc: Zoltán Böszörményi <zboszor@pr.hu>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>