wifi: ath6kl: replace deprecated strncpy with memcpy

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous
interfaces.

The affected code's purpose is to truncate strings that are too long
with "..." like:
foobar -> fo...

The lengths have been carefully calculated and as such this has decayed
to a simple byte copy from one buffer to another -- let's use memcpy().

Note: build-tested only.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://github.com/KSPP/linux/issues/90


Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20231013-strncpy-drivers-net-wireless-ath-ath6kl-init-c-v1-1-d69c599b49a9@google.com