Fix a kernel-doc warning of missing struct field desription:

../drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c:92: warning: Function parameter or member 'vm' not described in 'amdgpu_vm_eviction_lock'

Fixes: a269e449 ("drm/amdgpu: Avoid reclaim fs while eviction lock")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Signed-off-by: Alex Sierra <alex.sierra@amd.com>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: David (ChunMing) Zhou <David1.Zhou@amd.com>
Cc: amd-gfx@lists.freedesktop.org
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>