dt-bindings: net: bluetooth: qualcomm: document WCN3950

WCN3950 is another member of the WiFi/BT WCN39xx family of the chips. It
requires different firmware, so document it as a new compat string.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>