staging: wilc1000: move clean up codes into wl_wlan_cleanup function

This patch moves clean up codes from exit_wilc_driver into the wl_wlan_cleanup
newly introduced in this patch. In addition, it is called by linux_sdio_remove
function.

Signed-off-by: Tony Cho <tony.cho@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>