iwlagn: fix the race in the unmapping of the HCMD

As Stanislaw pointed out, my patch

	iwlagn: fix a race in the unmapping of the TFDs

solved only part of the problem. The race still exists for TFDs of
the host commands. Fix that too.

Reported-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>