IB/hfi1: Assign context does not clean up file descriptor correctly on error

In the error path for context allocation, the file descriptor pointer
should not point to a context when an error occurs.

Clean up the appropriate references on error.

Fixes: Commit 62239fc6

 ("IB/hfi1: Clean up on context initialization failure")
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>