[PATCH] clean up sd bdev methods

(1) move all bdev methods in one place instead of spreading them all
    around the file
(2) consistant naming: everything is sd_<operation> now
(3) use scsi_device_get/scsi_device_put
(4) remove bogus checks scsi_disk->device set, since 2.5.4x it always is
(5) clean up some coding style issues