sound/usb: call usb_autopm_get_interface() for devices that should not

be suspended

Webcams with microphones are composite devices, and autosuspend is set
at the device level. If uvcvideo is probed after snd-usb-audio, the effect
of the quirk applied by snd-usb-audio is undone by uvcvideo's global
application of autosuspend.

Incrementing the interface's PM refcount in such cases prevents runtime PM
from happening, thus the device is left active.

Signed-off-by: Jonathan Bell <jonathan@raspberrypi.com>