package/kernel: i2c: don't skip built-in modules

Don't skip build-in modules when generating i2c kmod packages, to allow
empty packages to be generated for satisfying dependencies.

Closes #12259.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@35755 3c298f89-4303-0410-b956-a3cf2f4a3e73