update compare function unit comment

From-SVN: r11566

gcc/config/rs6000/rs6000.md

@@ -200,11 +200,7 @@
   20 19)
 
 ; compare is done on integer unit, but feeds insns which
-; execute on the branch unit.  Ready-delay of the compare 
-; on the branch unit is large (3-5 cycles).  On the iu/fpu
-; it is 1.  One drawback is that the compare will also be 
-; assigned to the bpu, but this inaccuracy is worth for being
-; able to fill the compare-branch delay, with insns on iu/fpu.
+; execute on the branch unit.
 (define_function_unit "iu" 1 0   
   (and (eq_attr "type" "compare")
        (eq_attr "cpu" "rios1"))