dma-buf/sync_file: use strscpy to replace strlcpy

The strlcpy should not be used because it doesn't limit the source
length. Preferred is strscpy.

Signed-off-by: XueBing Chen <chenxuebing@jari.cn>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/6aad3bff.d1a.181b982d1b1.Coremail.chenxuebing@jari.cn