drm/amdgpu/jpeg: fix jpeg_v4_0_3_is_idle detection

drm/amdgpu/jpeg: fix jpeg_v4_0_3_is_idle detection

jpeg_v4_0_3_is_idle() initializes ret to false and then accumulates ring
idle status using &=. Since false & condition always remains false, the
function can never report the JPEG block as idle.

Initialize ret to true so the function returns true only when all JPEG
rings report RB_JOB_DONE.

Signed-off-by: Boyuan Zhang <boyuan.zhang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit e9df8e9d04e0593d17ddb069f3b7958991cd18c9)
Cc: stable@vger.kernel.org