Bluetooth: hci_qca: don't call pwrseq_power_off() twice for QCA6390

Now that we call pwrseq_power_off() for all models that hold a valid
power sequencing handle, we can remove the switch case for QCA_6390. The
switch will now use the default label for this model but that's fine: if
it has the BT-enable GPIO than we should use it.

Fixes: eba17187 ("Bluetooth: hci_qca: make pwrseq calls the default if available")
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>