md/raid5: Clear bad blocks on successful write.

On a successful write to a known bad block, flag the sh
so that raid5d can remove the known bad block from the list.

Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/raid5.h

@@ -274,6 +274,7 @@ struct stripe_head_state {
 #define	R5_Wantdrain	13	/* dev->towrite needs to be drained */
 #define	R5_WantFUA	14	/* Write should be FUA */
 #define	R5_WriteError	15	/* got a write error - need to record it */
+#define	R5_MadeGood	16	/* A bad block has been fixed by writing to it*/
 /*
  * Write method
  */