MAINTAINERS: add Chandan as xfs maintainer for 5.4.y

This is an attempt to direct the bots and humans that are testing
LTS 5.4.y towards the maintainer of xfs in the 5.4.y tree.

Update Darrick's email address from upstream and add Chandan as xfs
maintaier for the 5.4.y tree.

Suggested-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/linux-xfs/Yrx6%2F0UmYyuBPjEr@magnolia/


Acked-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandan.babu@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>