plugins/eis: Use monotonic clock to generate timestamps

(cherry picked from commit 1e29e7df82)

src/plugins/eis/eiscontext.cpp

@@ -108,7 +108,7 @@ int EisContext::addClient()
 
 static std::chrono::microseconds currentTime()
 {
-    return std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::system_clock::now().time_since_epoch());
+    return std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::steady_clock::now().time_since_epoch());
 }
 
 void EisContext::handleEvents()

src/plugins/eis/eisdevice.cpp

@@ -13,7 +13,7 @@ namespace KWin
 
 static std::chrono::microseconds currentTime()
 {
-    return std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::system_clock::now().time_since_epoch());
+    return std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::steady_clock::now().time_since_epoch());
 }
 
 EisDevice::EisDevice(eis_device *device, QObject *parent)