staging: wilc1000: change function to static in linux_wlan

Defined function as static which are used only in single file. And also removed
their declaration from header file.
Below function are changed to static
wilc_wlan_initialize()
wilc_wlan_deinitialize()
wilc_wlan_get_firmware()

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