Bluetooth: hci_qca: mark OF related data as maybe unused

The driver can be compile tested with !CONFIG_OF making certain data
unused:

  drivers/bluetooth/hci_qca.c:1869:37: error: ‘qca_soc_data_wcn6750’
  defined but not used [-Werror=unused-const-variable=]
  drivers/bluetooth/hci_qca.c:1853:37: error: ‘qca_soc_data_wcn3998’
  defined but not used [-Werror=unused-const-variable=]
  drivers/bluetooth/hci_qca.c:1841:37: error: ‘qca_soc_data_wcn3991’
  defined but not used [-Werror=unused-const-variable=]
  drivers/bluetooth/hci_qca.c:1830:37: error: ‘qca_soc_data_wcn3990’
  defined but not used [-Werror=unused-const-variable=]

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