target_files: copy to PRODUCT-SERVICES instead

The add_img_to_target_files.py script uses upper() to determine
the name of sub-directory under target_files_intermediates. The
name of the image is product-services.img but the sub-directory
name was PRODUCT_SERVICES. Change it to PRODUCT-SERVICES so that
'm dist' works.

Test: m dist
Change-Id: I8cad841c674b5d62c1d803d0383fc3aee14f272a