wifi: ray_cs: fix stringop-truncation GCC warning

GCC 12.2 with W=1 warns:

drivers/net/wireless/legacy/ray_cs.c:630:17: warning: 'strncpy' specified bound 32 equals destination size [-Wstringop-truncation]

The driver uses SSID as a string which is just wrong, it should be treated as a
byte array instead. But as the driver is ancient and most likely there are no
users so convert it to use strscpy(). This makes sure that the string is
NUL-terminated and also the warning is fixed.

Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230613140918.389690-5-kvalo@kernel.org