tools/zlib: fix PKG_CPE_ID
cpe:/a:zlib:zlib is the correct CPE ID for zlib:
https://nvd.nist.gov/products/cpe/search/results?keyword=cpe:2.3:a:zlib:zlib
Fixes: c61a2395140d92cdd37d3d6ee43a765427e8e318 (add PKG_CPE_ID ids to package and tools)
Signed-off-by: Fabrice Fontaine <[email protected]>