AIC7902 w/ seagate U320 drive issue on releng-4 (and current)

[Don Bowman]

> From: Don Bowman 

 ... [scsi errors with seagate cheetah on supermicro with adaptec aic7902]

I sometimes then get a panic due to this KASSERT in 
sys/ufs/ufs/ufs_readwrite.c:

                /*
                 * We should only get non-zero b_resid when an I/O error  
                 * has occurred, which should cause us to break above.  
                 * However, if the short read did not cause an error,
                 * then we want to ensure that we do not uiomove bad
                 * or uninitialized data.
                 *
                 * XXX b_resid is only valid when an actual I/O has occured
                 * and may be incorrect if the buffer is B_CACHE or if the

                 * last op on the buffer was a failed write.  This KASSERT  
                 * is a precursor to removing it from the UFS code.
                 */
                KASSERT(bp->b_resid == 0, ("bp->b_resid != 0"));