intel_th: Set root device's drvdata early

Already during the subdevice initialization time, devices will need
to reference Intel TH controller descriptor structure.

This patch moves setting the drvdata from the pci glue to intel_th
core, before subdevices are populated.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>