[SCSI] sd: remove arbitrary SD_MAX_DISKS namespace limit

There is no reason to limit the SCSI disk namespace to sdXXX.

Add new error messages to sd_probe() in the unlikely event that either
ida_get_new() or sd_format_disk_name() fail.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>