when the sg driver is unable to setup direct IO, free that scatter
gather list prior to falling back to indirect IO

Further to this thread started by Bryan Holty:
http://marc.theaimsgroup.com/?l=linux-scsi&m=114306885116728&w=2

Here is the reworked patch again. This time it has been
tested with a program provided by Bryan.
Signed-off-by: Douglas Gilbert <dougg@torque.net>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>