[SCSI] fix double free of scsi request queue

Current scsi scanning code appears to have a use after free
bug is a LLDD's slave_alloc fails. Remove the redundant
scsi_free_queue.

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