Fix RefCounter count return

Signed-off-by: Alfred Landrum <alfred.landrum@docker.com>

daemon/graphdriver/counter.go

@@ -40,8 +40,9 @@ func (c *RefCounter) Increment(path string) int {
 		}
 	}
 	m.count++
+	count := m.count
 	c.mu.Unlock()
-	return m.count
+	return count
 }
 
 // Decrement decreases the ref count for the given id and returns the current count
@@ -62,6 +63,7 @@ func (c *RefCounter) Decrement(path string) int {
 		}
 	}
 	m.count--
+	count := m.count
 	c.mu.Unlock()
-	return m.count
+	return count
 }