qcacld-3.0: Fix -Wmissing-prototypes in dph_hash_table

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

Change-Id: I9513060929343a61c329e55e15f7e6ec18d1e166
CRs-Fixed: 1075090

core/mac/src/dph/dph_hash_table.c

@@ -96,7 +96,8 @@ void dph_hash_table_class_init(tpAniSirGlobal pMac,
  * @return None
  */
 
-uint16_t hash_function(tpAniSirGlobal pMac, uint8_t staAddr[], uint16_t numSta)
+static uint16_t hash_function(tpAniSirGlobal pMac, uint8_t staAddr[],
+			      uint16_t numSta)
 {
 	int i;
 	uint16_t sum = 0;