ALSA: hda: Fix too short HDMI/DP chmap reporting

We got a regression report about the HD-audio HDMI chmap, where some
surround channels are reported as UNKNOWN.  The git bisection pointed
the culprit at the commit 9b3dc8aa ("ALSA: hda - Register chmap
obj as priv data instead of codec").  The story behind scene is like
this:

- While moving the code out of the legacy HDA to the HDA common place,
  the patch modifies the code to obtain the chmap array indirectly in
  a byte array, and it expands it to kctl value array.
- At the latter operation, the size of the array is wrongly passed by
  sizeof() to the pointer.
- It can be 4 on 32bit arch, thus too short for 6+ channels.
  (And that's the reason why it didn't hit other persons; it's 8 on
  64bit arch, thus it's usually enough.)

The code was further changed meanwhile, but the problem persisted.
Let's fix it by correctly evaluating the array size.

Fixes: 9b3dc8aa ("ALSA: hda - Register chmap obj as priv data instead of codec")
Reported-by: VDR User <user.vdr@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>