MAINTAINERS: erofs: update my email address

This email address will not be available in a few days.
Update my own email address to xiang@kernel.org, which
should be available all the time.

Link: https://lore.kernel.org/r/20200328040036.117974-1-gaoxiang25@huawei.com
Acked-by: Chao Yu <yuchao0@huawei.com>
Change-Id: Iec37d7160e6f7c82f0b0a3703ecd901f0b4e4b0e
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>

MAINTAINERS

@@ -5145,7 +5145,7 @@ F:	drivers/video/fbdev/s1d13xxxfb.c
 F:	include/video/s1d13xxxfb.h
 
 EROFS FILE SYSTEM
-M:	Gao Xiang <gaoxiang25@huawei.com>
+M:	Gao Xiang <xiang@kernel.org>
 M:	Chao Yu <yuchao0@huawei.com>
 L:	linux-erofs@lists.ozlabs.org
 S:	Maintained