Bluetooth: btusb: Fix atheros firmware download error

Move usb_autopm_get_interface() ahead of setup_on_usb() to prevent
device from sending usb control message in usb suspend mode.

The error message is as below:

[   83.944103] btusb 1-2:1.1: usb_suspend_interface: status 0
[   83.944107] btusb 1-2:1.0: usb_suspend_interface: status 0
[   83.960132] usb 1-2: usb auto-suspend, wakeup 0
[   83.976156] usb 1-2: usb_suspend_device: status 0
[   83.976162] usb 1-2: usb_suspend_both: status 0
[  298.689106] Bluetooth: hci0
[  298.689399] Bluetooth: hci0: Failed to access otp area (-113)

Signed-off-by: Ethan Hsieh <ethan.hsieh@canonical.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>