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 <swarren@nvidia.com>
Signed-off-by: Rob Herring <rob.herring@calxeda.com>

MAINTAINERS

@@ -6238,7 +6238,6 @@ OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS
 M:	Rob Herring <rob.herring@calxeda.com>
 M:	Pawel Moll <pawel.moll@arm.com>
 M:	Mark Rutland <mark.rutland@arm.com>
-M:	Stephen Warren <swarren@wwwdotorg.org>
 M:	Ian Campbell <ijc+devicetree@hellion.org.uk>
 M:	Kumar Gala <galak@codeaurora.org>
 L:	devicetree@vger.kernel.org