microblaze: Fix watchdog initialization

The patch:
"blackfin: Move blackfin watchdog driver out of the blackfin arch folder."
(sha1: e9a389a1)
changed hw_watchdog_init() prototype which didn't match
with Microblaze one.
This patch fixes the driver and Microblaze initialization.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>