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 <dzhu@wavecomp.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@linux-mips.org