Follow 0/-E convention for module load errors

Follow 0/-E convention for module load errors

Because errors during module load are so rare it went unnoticed that
it was possible that a positive errno was returned.  This would result
in the module being loaded, nothing being initialized, and a system
panic shortly thereafter.  This is what was causing the hard failures
in the automated testing.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>