IB/qib: Fix debugfs ordering issue with multiple HCAs

The debugfs init code was incorrectly called before the idr mechanism
is used to get the unit number, so the dd->unit hasn't been
initialized.  This caused the unit relative directory creation to fail
after the first.

This patch moves the init for the debugfs stuff until after all of the
failures and after the unit number has been determined.

A bug in unwind code in qib_alloc_devdata() is also fixed.

Cc: <stable@vger.kernel.org>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>