IB/hfi1: Correctly clear the pkey

In the close path the context is removed from the device array, and then
the clear pkey function is called.  The pkey function trys to get the
context from the device array, but because it was removed the clearing
does not occur.

Rework pkey clear function to work as expected.  Update the function
variable to reflect the correct size and name of the hw_context.

Reviewed-by: Mike Marciniszyn <mike.marciniszyn@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>