scsi: core: Unexport scsi_initialize_rq()

Commit 651a0136 ("scsi: scsi_transport_sas: switch to bsg-lib for
SMP passthrough") removed the only call to scsi_initialize_rq() from
outside the SCSI core. Hence unexport scsi_initialize_rq().

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