qcacld-3.0: Fix -Wmissing-prototypes in cfg_api

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

Change-Id: I6c282c78da047a9979b90c52fdcfd7b1b7b3b46e
CRs-Fixed: 1075090

core/mac/src/cfg/cfg_api.c

@@ -71,7 +71,7 @@ uint32_t cfg_need_restart(tpAniSirGlobal pMac, uint16_t cfgId)
 	return !!(pMac->cfg.gCfgEntry[cfgId].control & CFG_CTL_RESTART);
 }
 
-void cfg_get_strindex(tpAniSirGlobal pMac, uint16_t cfgId)
+static void cfg_get_strindex(tpAniSirGlobal pMac, uint16_t cfgId)
 {
 	uint16_t i = 0;