watchdog: bcm281xx: Fix use of uninitialized spinlock.

The bcm_kona_wdt_set_resolution_reg() call takes the spinlock, so
initialize it earlier.  Fixes a warning at boot with lock debugging
enabled.

Fixes: 6adb730d ("watchdog: bcm281xx: Watchdog Driver")
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
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>