编辑学校，上级组织添加清空按钮

src/components/schoolList.vue

@@ -247,7 +247,7 @@
 							<span>
 								<div class="add_input el-input el-input--suffix">
 									<el-form :model="school" ref="form">
-										<el-select v-model="school.parentOrgId" placeholder="请选择组织"
+										<el-select v-model="school.parentOrgId" clearable placeholder="请选择组织"
 											class="custom-select" filterable>
 											<el-option v-for="(org, index) in organizations" :key="index"
 												:label="org.name" :value="org.id">