scsi: Call scsi_initialize_rq() for filesystem requests

If a pass-through request is submitted then blk_get_request()
initializes that request by calling scsi_initialize_rq(). Also call this
function for filesystem requests. Introduce CMD_INITIALIZED to keep
track of whether or not a request has already been initialized.

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Brian King <brking@linux.vnet.ibm.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>