!317 【Form】修复icon被遮挡的问题

Merge pull request !317 from AlanLee/dev

Author: kagol

packages/devui-vue/devui/form/src/form-control/form-control.scss

@@ -12,7 +12,7 @@
  position: absolute;
  top: 50%;
  right: 0;
- z-index: 1;
+ z-index: 10;
  width: 32px;
  height: 16px;
  margin-top: -7px;