Revert to using memcpy().

This revert part of 4a0222.

src/iop/liquify.c

@@ -1309,8 +1309,8 @@ void process(struct dt_iop_module_t *module, dt_dev_pixelpipe_iop_t *piece, cons
     float *destrow = (float *)out + (size_t) ch * i * roi_out->width;
     const float *srcrow = (float *)in + (size_t) ch * (roi_in->width * (i + roi_out->y - roi_in->y) +
                                                        roi_out->x - roi_in->x);
-    for (int j=0; j < ch * roi_out->width; j++)
-      destrow[j] = srcrow[j];
+
+    memcpy (destrow, srcrow, sizeof (float) * ch * roi_out->width);
   }
 
   // 2. build the distortion map