staging: rtl8188eu: use strlcpy instead of strncpy

Use strlcpy instead of strncpy to avoid gcc 8 warning:
warning: '__builtin_strncpy' specified bound 16 equals destination size [-Wstringop-truncation]

The maximum length of the source string including terminating null is 5.
Hence it always fits in the destination buffer of length 16.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>