Fix bug introduced by:
commit 
2dde7861afa23cd59db83515cb0b810b92b220aa
Author: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Date:   Fri Apr 18 00:46:23 2008 +0200
    ide: rework PowerMac media-bay support (take 2)
...
[ Yeah, I suck. ]
bay->cd_index shouldn't be changed if IDE devices are not present
or retry operations won't happen.
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
                                printk("mediabay %d, registering IDE...\n", i);
                                pmu_suspend();
                                ide_port_scan(bay->cd_port);
-                               bay->cd_index = bay->cd_port->index;
+                               if (bay->cd_port->present)
+                                       bay->cd_index = bay->cd_port->index;
                                pmu_resume();
                        }
                        if (bay->cd_index == -1) {