try below
<input type="file" accept="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet, application/vnd.ms-excel" />
Or you could use javascript to check the file type
<script type="text/javascript" language="javascript">
function checkfile(sender) {
var validExts = new Array(".xlsx", ".xls");
var fileExt = sender.value;
fileExt = fileExt.substring(fileExt.lastIndexOf('.'));
if (validExts.indexOf(fileExt) < 0) {
alert("Invalid file selected, valid files are of " +
validExts.toString() + " types.");
return false;
}
else return true;
}
</script>
<input type="file" id="file" önchange="checkfile(this);" />