staging: rtl8192u: Fix big-endian warning

When compiling the rtl8192u driver from staging on a big-endian
architecture, the following warning results:

  CC [M]  drivers/staging/rtl8192u/ieee80211/ieee80211_softmac.o
drivers/staging/rtl8192u/ieee80211/ieee80211_softmac.c: In function 'ieee80211_probe_resp':
drivers/staging/rtl8192u/ieee80211/ieee80211_softmac.c:780: warning: value computed is not used

The warning is due to misuse of cpu_to_le16().

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>