brcmfmac: reinit watchdog completion after handling watchdog

The watchdog thread waits on completion that is set from a timer. As
the completion is count based this could mean that on a busy system
the watchdog is handled multiple times with a very short interval.
This is not the intended behaviour. After handling the watchdog it
should wait for the next timer expiry. This is accomplished by
reinitializing the completion.

Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>