pciutils: correct dns disabling logic

Fixes #8581

Commit 2c879f95 (pciutils: cleanup) refactored the make arguments, but
accidently changed the logic to disable dns based lookups to pass
PCIUTILS_DNS=no instead of DNS=no, causing the autotection to be used.

This autodetection looks at host includes, so it isn't safe for cross
compilation.

Disable it by setting the correct make variable instead.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>