ac97: don't override the pci subsystem id

This patch removes the code lines which set the subsystem id for the
emulated ac97 card to 8086:0000.  Due to the device id being zero the
subsystem id isn't vaild anyway.  With the patch applied the sound card
gets the default qemu subsystem id (1af4:1100) instead.

[ v2: old & broken id is maintained for -M pc-$oldqemuversion ]

Cc: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
