[SCSI] fix sense buffer length handling problem

The new bio code was incorrectly converted from stack allocated to
kmalloc'd buffer handling.  There are two places where it incorrectly
uses sizeof(*sense) to get the size of the sense buffer.  This
actually produces one, so no sense data was ever getting back, causing
failure in things like disk spin up.

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>