PackWriter: Fix Javadoc tag for thrown exception in preparePack

Use @throws instead of @param

Change-Id: Ic9419d254c617e60a9b10e49205b11069442eb27
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/pack/PackWriter.java

@@ -740,7 +740,7 @@ public class PackWriter implements AutoCloseable {
 	 *            Parents of {@code shallow} commits and earlier generations
 	 *            will be included in the pack if requested by {@code want}.
 	 *            Must not be {@code null}.
-	 * @param IOException
+	 * @throws IOException
 	 *            an I/O problem occured while reading objects.
 	 *
 	 * @since 4.5