iwlagn: move ucode_write_complete from priv to trans structure

ucode_write_complete is used for ucode loading.  Move it as part of
restructuring work out of the priv structure.

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>