usb: gadget: configfs: Replace strncpy with strlcpy

Use safer version of strcpy i.e. strlcpy instead of
strncpy for NULL terminated strings.

Change-Id: I5e2800d1d539545744a1b1231e1d589a7c92797a
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>