drm/amdgpu: Fix the warning info in mode1 reset

Fix the warning info below during mode1 reset.
[  +0.000004] Call Trace:
[  +0.000004]  <TASK>
[  +0.000006]  ? show_regs+0x6e/0x80
[  +0.000011]  ? __flush_work.isra.0+0x2e8/0x390
[  +0.000005]  ? __warn+0x91/0x150
[  +0.000009]  ? __flush_work.isra.0+0x2e8/0x390
[  +0.000006]  ? report_bug+0x19d/0x1b0
[  +0.000013]  ? handle_bug+0x46/0x80
[  +0.000012]  ? exc_invalid_op+0x1d/0x80
[  +0.000011]  ? asm_exc_invalid_op+0x1f/0x30
[  +0.000014]  ? __flush_work.isra.0+0x2e8/0x390
[  +0.000007]  ? __flush_work.isra.0+0x208/0x390
[  +0.000007]  ? _prb_read_valid+0x216/0x290
[  +0.000008]  __cancel_work_timer+0x11d/0x1a0
[  +0.000007]  ? try_to_grab_pending+0xe8/0x190
[  +0.000012]  cancel_work_sync+0x14/0x20
[  +0.000008]  amddrm_sched_stop+0x3c/0x1d0 [amd_sched]
[  +0.000032]  amdgpu_device_gpu_recover+0x29a/0xe90 [amdgpu]

This warning info was printed after applying the patch
"drm/sched: Convert drm scheduler to use a work queue rather than kthread".
The root cause is that amdgpu driver tries to use the uninitialized
work_struct in the struct drm_gpu_scheduler

v2:
 - Rename the function to amdgpu_ring_sched_ready and move it to
amdgpu_ring.c (Alex)
v3:
- Fix a few more checks based on Vitaly's patch (Alex)
v4:
- squash in fix noticed by Bert in
https://gitlab.freedesktop.org/drm/amd/-/issues/3139



Fixes: 11b3b9f4 ("drm/sched: Check scheduler ready before calling timeout handling")
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Signed-off-by: Ma Jun <Jun.Ma2@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>