mailmap: add entry for Barry Song

Include a .mailmap entry to synchronize with both my past and current
emails.  Among them, three business mailboxes are dead.

Link: https://lkml.kernel.org/r/20240506042009.10854-1-21cnbao@gmail.com
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>