staging: wilc1000: rename WILC_WFI_rates variable

This patch renames WILC_WFI_rates variable to ieee80211_bitrates
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>