drm/amdgpu: fix amdgpu_preempt_mgr_new()

There is a reversed if statement in amdgpu_preempt_mgr_new() so it
always returns -ENOMEM.

Fixes: 09b020bb ("Merge tag 'drm-misc-next-2021-06-09' of git://anongit.freedesktop.org/drm/drm-misc

 into drm-next")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/YMxbQXg/Wqm0ACxt@mwanda


Signed-off-by: Christian König <christian.koenig@amd.com>