PS3: Add repository polling loop to work around timing bug

On some firmware versions (e.g. 1.90), the storage device may not show up
in the repository immediately after receiving the notification message.
Add a small polling loop to make sure we don't miss it.

Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>