try this code...
for (UIView *searchbuttons in searchBar.subviews)
{
if ([searchbuttons isKindOfClass:[UIButton class]])
{
UIButton *cancelButton = (UIButton*)searchbuttons;
cancelButton.enabled = YES;
[cancelButton setBackgroundImage:[UIImage imageNamed:@"yourImageName"] forState:UIControlStateNormal];
break;
}
}