diag: dci: Return correct error status to client

After writing packet to SMD, diag driver is returning
wrong error status even in case of success which
leads to failure of dci client. This patch returns
correct error status to dci clients.

Change-Id: I1a9967c68c1e0a642b44f1d0ee1cc49f33f7ac91
Signed-off-by: Mohit Aggarwal <maggarwa@codeaurora.org>