dm: core: Drop use of strlcpy()

We can use printf() to limit the string width. Adjust the code to do this
instead of using strlcpy() which is a bit clumbsy.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>