staging: fsl-mc/dpio: Propagate error code

dpaa2_io_service_register() returns zero even if
qbman_swp_CDAN_set() encountered an error. Fix this
by propagating the error code so the caller is informed
data availability notifications are not properly set
for a channel.

Signed-off-by: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Acked-by: Bogdan Purcareata <bogdan.purcareata@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>