iwlwifi: move FW_ERROR to priv

The op_mode should check for FW_ERROR before calling send_cmd.  This
removes the need to test for FW_ERROR in the trans layer.

Signed-off-by: Don Fry <donald.h.fry@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>