MAINTAINERS: csky: Add mailing list for csky

Add mailing list and it's convenient for maintain C-SKY
subsystem.

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index a0d8649..a4b5858 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3649,6 +3649,7 @@
 
 C-SKY ARCHITECTURE
 M:	Guo Ren <guoren@kernel.org>
+L:	linux-csky@vger.kernel.org
 T:	git https://github.com/c-sky/csky-linux.git
 S:	Supported
 F:	arch/csky/