package/at-spi2-atk: add AT_SPI2_ATK_CPE_ID_VENDOR

cpe:2.3:a:gnome:at-spi2-atk is a valid CPE identifier for this package:

  https://nvd.nist.gov/products/cpe/search/results?namingFormat=2.3&keyword=cpe%3A2.3%3Aa%3Agnome%3Aat-spi2-atk



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