MAINTAINERS: remove swarren from DT bindings

I'm afraid I'm rather burned out w.r.t. DT bindings. As has probably
been evident, I don't have and haven't made the time to review many
recently. As such, remove myself from that MAINTAINERS entry.

Signed-off-by: Stephen Warren <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>

MAINTAINERS

···
 M:	Rob Herring <[e-mail]>
 M:	Pawel Moll <[e-mail]>
 M:	Mark Rutland <[e-mail]>
-M:	Stephen Warren <[e-mail]>
 M:	Ian Campbell <[e-mail]>
 M:	Kumar Gala <[e-mail]>
 L:	[e-mail]