amixer: expand local storage for item name according to kernel code

amixer: expand local storage for item name according to kernel code

According to kernel code (snd_ctl_elem_init_enum_names() in
sound/core/control.c), the maximum length of item name is 63 characters
(+ 1 terminator = 64 bytes). But current amixer implementation
uses 40 bytes. This causes name truncation and fail to operation.

This commit fixes this bug by expanding the length of local variables.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>