amixer: actually print all TLVs in a container TLV

amixer: actually print all TLVs in a container TLV

Due to a wrong indexing of tlv[] decode_tlv() always skips to the end of
the container TLV since the used tlv[1] contains the container TLV size
instead of the intended element size.

This causes, for example, only the first HDMI channel map TLV to be
shown.

Fix the indexing to actually use the element size.

Signed-off-by: Anssi Hannula <anssi.hannula@iki.fi>
Signed-off-by: Takashi Iwai <tiwai@suse.de>