[SCSI] ipr: Disk array rescanning fix

IPR RAID arrays show up on a virtual scsi bus, with a scsi bus number
of 255, which is generated by the adapter microcode. For the initial
scan of the host, we manually scan this bus since it does not obey
SAM in regards to sparse LUNs and the disk array devices do not have
a consistent product id to use scsi core's blacklist. If /proc/scsi/scsi
or sysfs is used to delete one of these devices, the device will not
be able to get added back by rescanning the host since scsi core
will see ipr's max_channel as 4, rather than 255. Update max_channel
after the initial scan so that ipr raid arrays can get re-added
if they get deleted.

Signed-off-by: Brian King <brking@us.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>