mixer-control: fix -Wsign-compare warnings

headset_card type is changed from int to guint32 to match uint32_t
used in PulseAudio's pa_card_info struct.
1 job for wip/muktupavels/warnings in 4 minutes and 57 seconds (queued for 1 second)
Status Name Job ID Coverage
  Test
passed build-fedora #665074

00:04:57