atiixp: SB700 contains more than one IDE channel

SB700 supports one physical IDE channel, but SB700 SATA controller
supports combined mode.  When the SATA combined mode is enabled,
two SATA ports (port4 and port5) share one IDE channel from IDE
controller, and PATA will share the other IDE channel.

Our previous patch adding SB700 IDE device ID only supports one
IDE channel, which contains bug.  The attached patch fixes the bug.

Signed-off-by: "Shane Huang" <Shane.Huang@amd.com>
Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>