drm/amdgpu: fix failure mapping legacy queue when FLR

Flag "mes.ring.shced.ready" will be set as true after mes hw init and set
as false when mes hw fini to avoid duplicate initialization. But hw fini
will not be called when function level reset, which will cause mes hw
init be skipped during FLR, which will leads to mapping legacy queue
fail. Set this flag as false when post reset will fix this issue.

Signed-off-by: Lin.Cao <lincao12@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>