staging, rtl8192e, LLVMLinux: Remove unused prototype

MgntQuery_MgntFrameTxRate is only used within rtllib_softmac.c, so it really
should be static instead of extern.

Since it is currently extern a warning is generated because a different
function of the same name is defined staticlly in ieee80211_softmac.c

Removing the incorrect extern declaration and defining the rtllib_softmac
version of this routine static fixes the warning.

Signed-off-by: Behan Webster <behanw@converseincode.com>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>