mesh: Fix uninitilized error

This fixes the following error:

mesh/cfgmod-server.c: In function ‘cfg_srv_pkt’:
mesh/cfgmod-server.c:103:5: error: ‘pub’ may be used uninitialized in
this function [-Werror=maybe-uninitialized]
diff --git a/mesh/cfgmod-server.c b/mesh/cfgmod-server.c
index e982c79..2c4a029 100644
--- a/mesh/cfgmod-server.c
+++ b/mesh/cfgmod-server.c
@@ -81,7 +81,7 @@
 	uint32_t mod_id;
 	uint16_t ele_addr;
 	int ele_idx;
-	struct mesh_model_pub *pub;
+	struct mesh_model_pub *pub = NULL;
 	int status;
 
 	if (size == 4)