drm/i915/gt: Only ignore already reset requests

If a request is being re-run after an innocent reset, it is marked as
-EAGAIN. So only skip an engine reset if the request is marked as -EIO.

Testcase: igt/gem_ctx_exec/basic-nohangcheck
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200207161602.2838218-1-chris@chris-wilson.co.uk