cmake: Fix VAPI .hpp generation

Change-Id: I2bec3b2511f00d017f9b3a727809631695222c1a
Signed-off-by: Mohsin Kazmi <sykazmi@cisco.com>
diff --git a/src/vpp-api/vapi/vapi_cpp_gen.py b/src/vpp-api/vapi/vapi_cpp_gen.py
index adf85c7..3260268 100755
--- a/src/vpp-api/vapi/vapi_cpp_gen.py
+++ b/src/vpp-api/vapi/vapi_cpp_gen.py
@@ -136,7 +136,7 @@
     print("#define %s" % include_guard)
     print("")
     print("#include <vapi/vapi.hpp>")
-    print("#include <%s%s>" % (gen_h_prefix, json_to_c_header_name(j)))
+    print("#include <%s%s>" % (gen_h_prefix, json_to_c_header_name(f)))
     print("")
     print("namespace vapi {")
     print("")