iwlwifi: move uCode deallocation to drv

This shouldn't be in the op_mode, as it
will later be switchable at runtime.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>