fix compile warning

bsp/raspberry-pi/raspi3-64/.project

-<?xml version="1.0" encoding="UTF-8"?>
-<projectDescription>
-  <name>raspi2</name>
-  <comment />
-  <projects>
-	</projects>
-  <buildSpec>
-    <buildCommand>
-      <name>org.eclipse.cdt.managedbuilder.core.genmakebuilder</name>
-      <triggers>clean,full,incremental,</triggers>
-      <arguments>
-			</arguments>
-    </buildCommand>
-    <buildCommand>
-      <name>org.eclipse.cdt.managedbuilder.core.ScannerConfigBuilder</name>
-      <triggers>full,incremental,</triggers>
-      <arguments>
-			</arguments>
-    </buildCommand>
-  </buildSpec>
-  <natures>
-    <nature>org.eclipse.cdt.core.cnature</nature>
-    <nature>org.eclipse.cdt.core.rttnature</nature>
-    <nature>org.eclipse.cdt.managedbuilder.core.managedBuildNature</nature>
-    <nature>org.eclipse.cdt.managedbuilder.core.ScannerConfigNature</nature>
-  </natures>
-  <linkedResources>
-    <link>
-      <name>rt-thread</name>
-      <type>2</type>
-      <locationURI>virtual:/virtual</locationURI>
-    </link>
-    <link>
-      <name>rt-thread/components</name>
-      <type>2</type>
-      <locationURI>$%7BPARENT-2-PROJECT_LOC%7D/components</locationURI>
-    </link>
-    <link>
-      <name>rt-thread/include</name>
-      <type>2</type>
-      <locationURI>$%7BPARENT-2-PROJECT_LOC%7D/include</locationURI>
-    </link>
-    <link>
-      <name>rt-thread/libcpu</name>
-      <type>2</type>
-      <locationURI>$%7BPARENT-2-PROJECT_LOC%7D/libcpu</locationURI>
-    </link>
-    <link>
-      <name>rt-thread/src</name>
-      <type>2</type>
-      <locationURI>$%7BPARENT-2-PROJECT_LOC%7D/src</locationURI>
-    </link>
-  </linkedResources>
-</projectDescription>