MAINTAINERS: Add Xinhui Pan as another AMDGPU contact

Since Chunming Zhou left AMD last year we are down to only
two maintainers once more. So add Xinhu Pan as another
contact as well.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Xinhui Pan <xinhui.pan@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210505110146.11689-1-christian.koenig@amd.com

MAINTAINERS

@@ -15272,6 +15272,7 @@ F:	drivers/net/wireless/quantenna
 RADEON and AMDGPU DRM DRIVERS
 M:	Alex Deucher <alexander.deucher@amd.com>
 M:	Christian König <christian.koenig@amd.com>
+M:	Pan, Xinhui <Xinhui.Pan@amd.com>
 L:	amd-gfx@lists.freedesktop.org
 S:	Supported
 T:	git https://gitlab.freedesktop.org/agd5f/linux.git