rio: warn_unused_result warnings fix

Adding failure path for the following two cases.

warning: ignoring return value of 'device_add', declared with attribute warn_unused_result
warning: ignoring return value of 'sysfs_create_bin_file', declared with attribute warn_unused_result

Signed-off-by: Li Yang <leoli@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>