staging: wilc1000: wilc_spi.c: add prefix wilc in all function name

This patch add prefix wilc for all functions name because the function name
such as spi_write, spi_read and spi_sync are same as linux spi function.
Hence, this should be done before restructuring wilc_spi.c and
linux_wlan_spi.c later.

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