staging: rtl8192u: make in ieee80211/ieee80211_wx.c a local variable static

Make some local variable eee80211_modes static.

Fix sparse warnings:
drivers/staging/rtl8192u/ieee80211/ieee80211_wx.c:42:19: warning: symbol 'ieee80211_modes' was not declared. Should it be static?

Signed-off-by: Ana Rey <anarey@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>