wifi: rtl8xxxu: Use strscpy instead of sprintf

Fill priv->chip_name and priv->chip_vendor with strscpy instead of
sprintf. This is just to prevent future bugs in case the name of a
chip/vendor becomes longer than the size of chip_name/chip_vendor.

Suggested-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/5fc9cc0e-eecb-8428-aeb1-f745791c0f16@gmail.com