qcacld-3.0: Fix -Wmissing-prototypes in lim_process_probe_req_frame

We want to enable the compiler's -Wmissing-prototypes switch, but
there is existing code that is generating warnings. Fix all warnings
in lim_process_probe_req_frame.

Change-Id: I8d253570f1ab52b52964a6ff67477f7150d39e5d
CRs-Fixed: 1075090

core/mac/src/pe/lim/lim_process_probe_req_frame.c

@@ -312,7 +312,7 @@ void lim_wpspbc_close(tpAniSirGlobal pMac, tpPESession psessionEntry)
  * @return BOOLEAN
  */
 
-bool lim_check11b_rates(uint8_t rate)
+static bool lim_check11b_rates(uint8_t rate)
 {
 	if ((0x02 == (rate))
 	    || (0x04 == (rate))