maintainers: Add Lei YU as maintainer

Lei has been an active reviewer for sdbusplus, and fixed the CI issue
that has been there for quite a while.

He is willing to become one of the maintainers for sdbusplus, which is
good for speed up the review progress, and for redundancy.

Signed-off-by: Lei YU <mine260309@gmail.com>
Change-Id: I39ec5a1adc0d34c4ce2919a92bd7df463818b9d6
diff --git a/MAINTAINERS b/MAINTAINERS
index b694c5a..d648b8b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -44,6 +44,7 @@
 
 M:  William Kennington <wak@google.com> <wak-work!>
 M:  Vernon Mauery <vernon.mauery@linux.intel.com> <vmauery!>
+M:  Lei Yu <mine260309@gmail.com> <LeiYU!>
 R:  Brad Bishop <bradleyb@fuzziesquirrel.com> <radsquirrel!>
 R:  Adriana Kobylak <anoo@us.ibm.com> <anoo!>
 R:  Deepak Kodihalli <dkodihal@in.ibm.com> <dkodihal!>