staging:rtl8192u:ieee80211: Fix smatch warning of function definition with external linkage

This patch fixes the warnings:
drivers/staging/rtl8192u/ieee80211/ieee80211_tx.c:381:13: warning: function 'ieee80211_qurey_ShortPreambleMode' with external linkage has definition
drivers/staging/rtl8192u/ieee80211/ieee80211_tx.c:395:1: warning: function 'ieee80211_query_HTCapShortGI' with external linkage has definition

Signed-off-by: Himangi Saraogi <himangi774@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>