contrib/samplerate: disable building tests, doc, examples

make build faster by disabling the build of
doc, examples and tests subdirectories.
Also prevent potential build errors in those directories.

Change-Id: I14e5d62831301227c7250a3aaef55db20e8343c2
Reviewed-by: Guillaume Roguez <guillaume.roguez@savoirfairelinux.com>