tests/check/: Fix big batch of compiler warnings.

tests/check/: Fix big batch of compiler warnings.

Original commit message from CVS:
* tests/check/elements/audioresample.c: (GST_START_TEST):
* tests/check/elements/videotestsrc.c: (check_rgb_buf):
* tests/check/elements/volume.c: (GST_START_TEST):
* tests/check/elements/vorbisdec.c: (GST_START_TEST):
* tests/check/pipelines/oggmux.c: (validate_ogg_page), (eos_watch),
(test_pipeline), (GST_START_TEST):
* tests/check/pipelines/theoraenc.c: (GST_START_TEST):
* tests/check/pipelines/vorbisenc.c: (GST_START_TEST):
Fix big batch of compiler warnings.