Qualcomm ROME controllers can be registered from the Bluetooth line
discipline and in this case the HCI UART serdev pointer is NULL.

Add the missing sanity check to prevent a NULL-pointer dereference when
wakeup() is called for a non-serdev controller during suspend.

Just return true for now to restore the original behaviour and address
the crash with pre-6.2 kernels, which do not have commit e9b3e5b8
("Bluetooth: hci_qca: only assign wakeup with serial port support") that
causes the crash to happen already at setup() time.

Fixes: c1a74160 ("Bluetooth: hci_qca: Add device_may_wakeup support")
Cc: stable@vger.kernel.org      # 5.13
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>