mailmap: Update name spelling and email for Dengcheng Zhu

Change my first name spelling from Deng-Cheng to Dengcheng.

Update email addresses.

Signed-off-by: Dengcheng Zhu <[e-mail]>
Signed-off-by: Paul Burton <[e-mail]>
Cc: [e-mail]

.mailmap

···
 Damian Hobson-Garcia <[e-mail]>
 David Brownell <[e-mail]>
 David Woodhouse <[e-mail]>
-Deng-Cheng Zhu <[e-mail]> <[e-mail]>
+Dengcheng Zhu <[e-mail]> <[e-mail]>
+Dengcheng Zhu <[e-mail]> <[e-mail]>
+Dengcheng Zhu <[e-mail]> <[e-mail]>
+Dengcheng Zhu <[e-mail]> <[e-mail]>
 Dmitry Eremin-Solenikov <[e-mail]>
 Domen Puncer <[e-mail]>
 Douglas Gilbert <[e-mail]>