QStorageInfo/Linux: move from MountInfo's contents

Copying QStrings and QByteArrays is reasonably cheap, but moving is
cheaper.

Pick-to: 6.6
Change-Id: I9d43e5b91eb142d6945cfffd1787498ead687da2
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>

src/corelib/io/qstorageinfo_linux.cpp

@@ -149,10 +149,10 @@ void QStorageInfoPrivate::initRootPath()
         }
     }
     if (bestInfo) {
-        rootPath = bestInfo->mountPoint;
-        device = bestInfo->device;
-        fileSystemType = bestInfo->fsType;
-        subvolume = bestInfo->fsRoot;
+        rootPath = std::move(bestInfo->mountPoint);
+        device = std::move(bestInfo->device);
+        fileSystemType = std::move(bestInfo->fsType);
+        subvolume = std::move(bestInfo->fsRoot);
     }
 }