Use uint8_t* for BS buffers in OSD

src/osd/osd_flush.cpp

@@ -189,7 +189,7 @@ bool osd_t::submit_flush_op(pool_id_t pool_id, pg_num_t pg_num, pg_flush_batch_t
             {
                 .len = (uint32_t)count,
             },
-            .buf = op->buf,
+            .buf = (uint8_t*)op->buf,
         });
         bs->enqueue_op(op->bs_op);
     }