Input: wacom_w8001 - replace strlcat() with a strscpy() helper

In preparation for removing the strlcat() API[1], replace its five
uses with a small append helper built on strnlen() and strscpy().

The five calls append device name fragments to a basename buffer
that grows in place across the setup functions. The helper takes
the same arguments as strlcat() and writes the same bytes, including
when a fragment is truncated.

Link: https://github.com/KSPP/linux/issues/370 [1]
Signed-off-by: Ian Bridges <icb@fastmail.org>
Link: https://patch.msgid.link/albg4Rv7QxvLJD05@dev
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>