Fix missing early return() in xxx_not_found() dependency macros.

- This could result in potentially confusing output if dependencies
  were found with the QUIET option: "XXX not found due to ...", followed
  by "found <part of> XXX".
- If find_package() was called with REQUIRED, then a FATAL_ERROR was
  triggered in the xxx_not_found() macros, resulting in early
  termination.

Change-Id: Ibf59afd10067b9debd1a5e15f735a41b61bed52e