staging: wilc1000: move static variable 'wlan_channel' to 'wilc' struct

Avoid use of static variable 'wlan_channel' by moving it inside the wilc
structure.

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>