RefDirectoryTest: Fix warning about member variable hiding

The parameter name 'totalWork' was hiding a class member variable
of the same name.

Change-Id: I646525e82900e23ffabfc756bcf5052ef873656a
Signed-off-by: David Pursehouse <david.pursehouse@sonymobile.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/RefDirectoryTest.java

@@ -1444,8 +1444,8 @@ public class RefDirectoryTest extends LocalDiskRepositoryTestCase {
 			// empty
 		}
 
-		public void beginTask(String title, int totalWork) {
-			this.totalWork = totalWork;
+		public void beginTask(String title, int total) {
+			this.totalWork = total;
 			lastWork = 0;
 		}