Fix iosched warning when using CFQ
    
    bios may not have an I/O context when we go to handle them. When using
    CFQ, submitting these directly to the original MRF results in this
    unhelpful message:
    
      __get_request: dev 8:0: request aux data allocation failed, iosched may be disturbed
    
    Create or get the I/O context before submitting.