Fix non-existing modules check

This variable was accidentally changed to refer to the
shorthand PRODUCT_XYZ instead of PRODUCTS.<mk>.PRODUCT_XYZ
in a previous mass-migration, but that shorthand didn't
exist for these variables. Add it in.

Also whitelist the offender introduced since it was broken.

Test: lunch generic; m nothing
Change-Id: I29dd73c29796743e770afa0c2ceb4f8583dc6e1e