Unfortunately HTML5 spec doesn't provide a way to define a date format, which is, to be honest a very bad decision on their side.
You can always use a 3rd party date picker's for jQuery Mobile.
Only 3 of them are wort mentioning, and every one can be configured to show certain date format and every one of them works on all devices. Thou I would recommend you Mobiscroll because it has skins that looks like native mobile/desktop datepickers.
Mobiscroll - http://jsfiddle.net/Gajotres/WDjfR/
$(document).on('pagebeforeshow', '#index', function(){
$('#demo').mobiscroll().date({
invalid: { daysOfWeek: [0, 6], daysOfMonth: ['5/1', '12/24', '12/25'] },
theme: 'android-ics',
display: 'inline',
mode: 'scroller',
dateOrder: 'dd mm yy',
dateFormat : "dd-mm-yy"
});
});
Mobipick - http://jsfiddle.net/Gajotres/zyVjE/
$(document).on('pagebeforeshow', '#index', function(){
$('#demo').mobipick({
dateFormat: "MM-dd-yyyy"
});
});
Datebox - http://jsfiddle.net/Gajotres/ktbcP/
<input name="mydate" id="mydate" type="date" data-role="datebox" data-options='{"mode": "datebox", "useNewStyle":true, "dateFormat": "mm/dd/YYYY"}'/>
If you want to find more about jQuery Mobile date pickers take a look at this article.