ath25: fix ELF image generation

ath25: fix ELF image generation

Commit 21f460a5dbef ("ath25: fix duplicate LZMA compression"), when
attempting to restore ELF artifact generation, copiedover the raw
kernel image twice. Because of that, the .elf artifact was actually a
duplicate of raw image.

Fix that by copying over .elf suffixed kernel image instead.

Fixes: 21f460a5dbef ("ath25: fix duplicate LZMA compression")
Signed-off-by: Lech Perczak <lech.perczak@gmail.com>
(cherry picked from commit 611291383a826827f240eddebca1949c2e1e7115)