MAINTAINERS: Update AMDGPU DML maintainers info

Chaitanya is no longer with AMD, and the responsibility has been
taken over by Austin.

Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: Aurabindo Pillai

MAINTAINERS

@@ -1053,7 +1053,7 @@ T:	git https://gitlab.freedesktop.org/agd5f/linux.git
 F:	drivers/gpu/drm/amd/display/
 
 AMD DISPLAY CORE - DML
-M:	Chaitanya Dhere <chaitanya.dhere@amd.com>
+M:	Austin Zheng <austin.zheng@amd.com>
 M:	Jun Lei <jun.lei@amd.com>
 S:	Supported
 F:	drivers/gpu/drm/amd/display/dc/dml/