iwlwifi: rename ucode.h to fw-file.h

That name better reflects the contents
of the file and the fact that it isn't
related to iwl-ucode.c.

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>