Couchbase: fix no previous prototype for ... [-Wmissing-prototypes]

Change-Id: Ieaefb9d50bf0224f4e90585d138867d0b88d5814
Reviewed-on: https://code.wireshark.org/review/4956
Reviewed-by: Evan Huus <eapache@gmail.com>

epan/dissectors/packet-couchbase.c

@@ -215,6 +215,9 @@
  /* Data Types */
 #define DT_RAW_BYTES          0x00
 
+void proto_register_couchbase(void);
+void proto_reg_handoff_couchbase(void);
+
 static int proto_couchbase = -1;
 
 static int hf_magic = -1;