staging: wilc1000: remove function pointer io_init

This patch removes function pointer io_init of wilc_wlan_io_func_t and it's
related codes, and call the function linux_spi_init directly.

Signed-off-by: Glen Lee <glen.lee@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>