rocker: fix non-portable err return codes

The rocker device returns error codes if something goes wrong with descriptor
processing.  Originally the device used standard errno codes for different
errors, but since those errno codes aren't portable across ARCHs, the device
now returns hard-coded error codes that stay constant across diff ARCHs.  Fix
driver to use those same hard-coded values.

Signed-off-by: Scott Feldman <sfeldma@gmail.com>
Acked-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>