iwlwifi: calculate pointers from out_cmd instead of out_cmd->hdr

The out_cmd structure starts with a header, so there's no need to use
&out_cmd->hdr, out_cmd alone is enough.  We use this when calculating
other addresses and klocwork gets confused with that because it thinks
we are trying to access hdr (as an array) beyond its size.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>