[AE] ALSA: Fix DeviceChange event triggered by enumeration

All hctl elements get an SND_CTL_EVENT_MASK_REMOVE event when the ctl
file descriptor is closed, which is done e.g. when re-enumerating
devices.

(SND_CTL_EVENT_MASK_REMOVE & SND_CTL_EVENT_MASK_VALUE) is true, and
therefore we re-triggered enumeration (depending a bit on timing).

Fix that by checking for the special _REMOVE value first and ignoring
those events.