Fix where the #ifdef CFG_BOOTMAPSZ is placed.

Commit 073e1b50 "Fix initrd/dtb
interaction" put the new code outside of the #if defined(CONFIG_OF_LIBFDT)
when it should have gone inside of the conditional.  As a result, it
broke non-LIBFDT board builds.

Also added a missing "not." to the comment.

Signed-off-by: Gerald Van Baren <vanbaren@cideas.com>