staging: wilc1000: Remove unused mutex cfg_values_lock

After removing cfg_values member, cfg_values_lock that was used to protect
it can also be removed.

Signed-off-by: Adham Abozaeid <adham.abozaeid@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>