eicon: fix -Warray-bounds warning

Fix for a -Warray-bounds warning. mixer_notify_update() tries to
write to ((CAPI_MSG *) msg)->info.facility_req.structs[3] while
structs is defined as byte structs[1]. Set all 'structs' which are
part of the typdefs in the info union to 'byte structs[0]'.

v2: set all info.*.structs to byte structs[0]

Signed-off-by: Danny Kukawka <danny.kukawka@bisect.de>
Signed-off-by: David S. Miller <davem@davemloft.net>