wifi: iwlwifi: return a new allocation for hdr page space

Instead of returning the pointer to the structure describing the header
page, return the pointer to the newly allocated area. This disentangles
the user from the allocation within the page as it does not need to
advance the position itself.

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Link: https://patch.msgid.link/20240703125541.044f2cb373f1.I52a807ac6f311b89530e18deacc7452638a6f5d8@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>