Fix regression taht caused usbms based drivers to not get correct timestamp for files on device

src/calibre/devices/usbms/books.py

@@ -38,8 +38,10 @@ class Book(MetaInformation):
             self.lpath = lpath
         self.mime = mime_type_ext(path_to_ext(lpath))
         self.size = size # will be set later if None
+        try:
+            self.datetime = time.gmtime(os.path.getctime(self.path))
+        except:
             self.datetime = time.gmtime()
-
         if other:
             self.smart_update(other)