ALSA: hda: controller code - do not export static functions

It is a bad idea to export static functions. GCC for some platforms
shows errors like:

  error: __ksymtab_azx_get_response causes a section type conflict

Signed-off-by: Jaroslav Kysela <perex@perex.cz>
Cc: <stable@vger.kernel.org> # v3.15+
Signed-off-by: Takashi Iwai <tiwai@suse.de>