package/protobuf-c: add PROTOBUF_C_CPE_ID_VENDOR

cpe:2.3:a:protobuf-c_project:protobuf-c is a valid CPE identifier for
this package:

  https://nvd.nist.gov/products/cpe/search/results?namingFormat=2.3&keyword=cpe%3A2.3%3Aa%3Aprotobuf-c_project%3Aprotobuf-c

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/protobuf-c/protobuf-c.mk

@@ -13,6 +13,7 @@ PROTOBUF_C_CONF_OPTS = --disable-protoc
 PROTOBUF_C_INSTALL_STAGING = YES
 PROTOBUF_C_LICENSE = BSD-2-Clause
 PROTOBUF_C_LICENSE_FILES = LICENSE
+PROTOBUF_C_CPE_ID_VENDOR = protobuf-c_project
 PROTOBUF_C_AUTORECONF = YES
 HOST_PROTOBUF_C_AUTORECONF = YES