ALSA: hda - fix sparse warning

Fix the following sparse warning:

sound/pci/hda/patch_nvhdmi.c:161:25: warning: symbol
'snd_hda_preset_nvhdmi' was not declared. Should it be static?

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>