watchdog: bcm2835_wdt: remove redundant ->set_timeout callback

bcm2835_wdt_set_timeout does exactly what the watchdog framework does
in the absence of a ->set_timeout callback (see watchdog_set_timeout
in watchdog_dev.c), so remove it.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>