Bluetooth: btusb: Fix triggering coredump implementation for QCA

btusb_coredump_qca() uses __hci_cmd_sync() to send a vendor-specific
command to trigger firmware coredump, but the command does not
have any event as its sync response, so it is not suitable to use
__hci_cmd_sync(), fixed by using __hci_cmd_send().

Fixes: 20981ce2

 ("Bluetooth: btusb: Add WCN6855 devcoredump support")
Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>