package/flex: set FLEX_CPE_ID_VALID

cpe:2.3:a:flex_project:flex is a valid CPE identifier for this package:

  https://nvd.nist.gov/products/cpe/search/results?namingFormat=2.3&keyword=cpe%3A2.3%3Aa%3Aflex_project%3Aflex

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/flex/flex.mk

@@ -9,6 +9,7 @@ FLEX_SITE = https://github.com/westes/flex/files/981163
 FLEX_INSTALL_STAGING = YES
 FLEX_LICENSE = FLEX
 FLEX_LICENSE_FILES = COPYING
+FLEX_CPE_ID_VALID = YES
 FLEX_DEPENDENCIES = $(TARGET_NLS_DEPENDENCIES) host-m4
 HOST_FLEX_DEPENDENCIES = host-m4