cosmetic: FIT: fix a strange comment

There is a strange comment in fit_image_load().
This function can be used for loading Kernel Image, FDT
as well as ramdisk.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Simon Glass <sjg@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org>