IB/hfi1: Remove kobj from hfi1_devdata

IB/hfi1: Remove kobj from hfi1_devdata

The field kobj was added to hfi1_devdata structure to manage the life time
of the hfi1_devdata structure for PSM accesses:

commit e11ffbd57520 ("IB/hfi1: Do not free hfi1 cdev parent structure early")

Later another mechanism user_refcount/user_comp was introduced to provide
the same functionality:

commit acd7c8fe1493 ("IB/hfi1: Fix an Oops on pci device force remove")

This patch will remove this kobj field, as it is no longer needed.

Link: https://lore.kernel.org/r/20200316210500.7753.4145.stgit@awfm-01.aw.intel.com
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Kaike Wan <kaike.wan@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>