drm/msm/dp: fix parsing of AUX switch device node

Fix the parsing of the AUX switch device node by removing unnecessary
parsing of the corresponding platform device. This fix enables access
to the AUX switch driver which is used to program the AUX switch.

Change-Id: I16ef1e314e411c9a2815dd3c8b23982e9e9d6599
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>