watchdog_v2: enqueue deferred work on current cpu instead of cpu0

Current implementation of deferring work in watchdog driver is tied
to cpu0 which prevents hotplugging cpu0. Modify this to schedule
deferred work on current cpu.

Change-Id: Idaf758430490163a94872ae11f0cea999198f4fb
Signed-off-by: Aparna Das <adas@codeaurora.org>