staging/rdma/hfi1: fix pio progress routine race with allocator

The allocation code assumes that the shadow ring cannot
be overrun because the credits will limit the allocation.

Unfortuately, the progress mechanism in sc_release_update() updates
the free count prior to processing the shadow ring, allowing the
shadow ring to be overrun by an allocation.

Reviewed-by: Mark Debbage <mark.debbage@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>