idmap2: fix cpplint warnings

Bug: 189963636
Test: frameworks/base/cmds/idmap2/static-checks.sh
Change-Id: I6da18cdbbd2fc33db711696445230a9f316dc143
diff --git a/cmds/idmap2/tests/IdmapTests.cpp b/cmds/idmap2/tests/IdmapTests.cpp
index 9516ff8..9c6402a 100644
--- a/cmds/idmap2/tests/IdmapTests.cpp
+++ b/cmds/idmap2/tests/IdmapTests.cpp
@@ -83,7 +83,7 @@
   std::stringstream stream;
   stream << android::kIdmapMagic;
   stream << 0xffffffffU;
-  stream << std::string(kJunkSize, (char)0xffU);
+  stream << std::string(kJunkSize, static_cast<char>(0xffU));
   ASSERT_FALSE(Idmap::FromBinaryStream(stream));
 }
 
@@ -92,7 +92,7 @@
   std::stringstream stream;
   stream << 0xffffffffU;
   stream << android::kIdmapCurrentVersion;
-  stream << std::string(kJunkSize, (char)0xffU);
+  stream << std::string(kJunkSize, static_cast<char>(0xffU));
   ASSERT_FALSE(Idmap::FromBinaryStream(stream));
 }