staging/gdm72xx: usb_boot: replace firmware upgrade API in em_download

Replace firmware upgrade API in em_download_image().

Signed-off-by: Macpaul Lin <macpaul@gmail.com>
Cc: Paul Stewart <pstew@chromium.org>
Cc: Ben Chan <benchan@chromium.org>
Cc: Sage Ahn <syahn@gctsemi.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>