MAINTAINERS: Add my hexagon git tree

Add my git tree for hexagon.  Note that the branch is "hex-next" and not
"hex.next" as had been used previously.  But I'll keep the "hex.next" branch
in sync with "hex-next" until this commit lands to avoid confusion.

Signed-off-by: Brian Cain <bcain@quicinc.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
diff --git a/MAINTAINERS b/MAINTAINERS
index 74a8536..10af212 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -245,6 +245,7 @@
 F: configs/targets/hexagon-linux-user/default.mak
 F: docker/dockerfiles/debian-hexagon-cross.docker
 F: gdb-xml/hexagon*.xml
+T: git https://github.com/quic/qemu.git hex-next
 
 Hexagon idef-parser
 M: Alessandro Di Federico <ale@rev.ng>