[SCSI] usb storage: use scsi_eh API in REQUEST_SENSE execution

  - Use new scsi_eh_prep/restor_cmnd() for synchronous
    REQUEST_SENSE invocation.

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>