powerpc/spufs: Fix coredump of SPU contexts

commit 99acc9be upstream.

If a process dumps core while it has SPU contexts active then we have
code to also dump information about the SPU contexts.

Unfortunately it's been broken for 3 1/2 years, and we didn't notice. In
commit 7b1f4020 ("spufs: get rid of dump_emit() wrappers") the nread
variable was removed and rc used instead. That means when the loop exits
successfully, rc has the number of bytes read, but it's then used as the
return value for the function, which should return 0 on success.

So fix it by setting rc = 0 before returning in the success case.

Fixes: 7b1f4020 ("spufs: get rid of dump_emit() wrappers")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

arch/powerpc/platforms/cell/spufs/coredump.c

@@ -174,6 +174,8 @@ static int spufs_arch_write_note(struct spu_context *ctx, int i,
 	if (!dump_skip(cprm,
 		       roundup(cprm->written - total + sz, 4) - cprm->written))
 		goto Eio;
+
+	rc = 0;
 out:
 	free_page((unsigned long)buf);
 	return rc;