staging: exfat: clean up d_entry rebuilding.

Clean up d_entry rebuilding in exfat_rename_file() and move_file().

-Replace memcpy of d_entry with structure copy.
-Change to use the value already stored in fid.

Signed-off-by: Tetsuhiro Kohada <Kohada.Tetsuhiro@dc.MitsubishiElectric.co.jp>
Acked-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Link: https://lore.kernel.org/r/20200302095716.64155-1-Kohada.Tetsuhiro@dc.MitsubishiElectric.co.jp


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>