Fix 6319: Table/ColToggle - setting display:block to override offset on fieldset

@uGoMobi:

This fixes #6319.

The fieldset inside the popup columntoggle already has: `margin: 0` set, but it also gets
````
.ui-mobile fieldset {
    display: table-column;
}
````
which causes a few pixels offset on the bottom of the popup.

Setting `display: block` in addition to margin fixes this.