Fix `exit` order to match reverse of `init`

This commit resolve the ordering of 'exit' dependencies as was started for 'init' in https://github.com/libusb/libusb/commit/0846456f3a9fda8ff5469d9d0b9700837ff16f04

(Relates to https://github.com/xloem/libusb/pull/5)

Closes #1126

Signed-off-by: Nathan Hjelm <hjelmn@google.com>