drm/amdgpu: Fix the lpfn checking condition in drm buddy

Because the value of man->size is changed during suspend/resume process,
use mgr->mm.size instead of man->size here for lpfn checking.

Signed-off-by: Ma Jun <Jun.Ma2@amd.com>
Suggested-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220914125331.2467162-1-Jun.Ma2@amd.com


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