iwlwifi: fix host command header according the HW spec

This patch aligns definition of host command with the spec. The
inaccuracies weren't critical though.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>