staging: wilc1000: renames u8IfIdx of wilc_vif structure

This patch renames u8IfIdx variable of wilc_vif structure to idx
to avoid camelcase.

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