The transport registration may fail.  Make sure the errors are propagated
to the callers.

Link: https://lore.kernel.org/r/20200106185817.640331-3-krisman@collabora.comReviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>