filters: linear_threads: Propagate errno.
filters: linear_threads: Propagate errno.

Since errno is per-thread variable we have to propagate it correctly on
a failure. This fixes api_coverate test failures for filters.

Signed-off-by: Cyril Hrubis <b1e90efd3b808b8e0bcf2a9a55fd8b9a779bfd81@ucw.cz>

gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim