watchdog: wafer5823wdt: Fix handling WDIOS_DISABLECARD/WDIOS_ENABLECARD options

While receiving WDIOS_DISABLECARD option for WDIOC_SETOPTIONS command,
call wafwdt_stop() to disable watchdog.
Call wafwdt_start() while receiving WDIOS_ENABLECARD option.

Current code has reverse behavior.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>