tree-test: Don't return restricted exit codes

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
base64-test: Remove posibility of returning restricted exit codes

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
dct-test: Remove possibility of returning a restricted exit code

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
fft-test: Remove possibility of returning restricted exit code

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>