staging: wilc1000: clean up timer feature

The driver has a simple wrapper around timer_list, and an
optional but unused feature to make the timer periodic.

This removes support for the periodic timer and simplifies
the code around timers.

A follow-up should replace the remaining wrapper with
open-coded timers.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>