iwlagn: remove knowledge of ucode image location from upper layers

The upper layers of the driver do not need to know where the ucode is
stored.  It already passes in an enum of which ucode to load.  Let the
lower layer routines select the ucode to load.

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>