crypto: scompress - return proper error code for allocation failure

If scomp_acomp_comp_decomp() fails to allocate memory for the
destination then we never copy back the data we compressed.
It is probably best to return an error code instead 0 in case of
failure.
I haven't found any user that is using acomp_request_set_params()
without the `dst' buffer so there is probably no harm.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>