Right now the pcap core driver passes a reference to its pcap data abusing the
subdrivers platform drvdata, this is not good.

Get the reference directly from the parent device.
Signed-off-by: Antonio Ospite <ospite@studenti.unina.it>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>