drm/amdgpu: set an error on all fences from a bad context

When we backup ring contents to reemit after a queue reset,
we don't backup ring contents from the bad context.  When
we signal the fences, we should set an error on those
fences as well.

v2: misc cleanups
v3: add locking for fence error, fix comment (Christian)
v4: fix wrap around, locking (Christian)

Fixes: 77cc0da3 ("drm/amdgpu: track ring state associated with a fence")
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>