ALSA: hda - fix DisplayPort naming

DisplayPort is a digital display interface standard put forth by
the Video Electronics Standards Association (VESA). It defines a
new license-free, royalty-free, digital audio/video interconnect,
intended to be used primarily between a computer and its display monitor,
or a computer and a home-theater system.

				- From Wikipedia, the free encyclopedia

Signed-off-by: Wu Fengguang <wfg@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>