drm/amdgpu: return early for non-TTM_PL_TT type BOs

Return early for non-TTM_PL_TT BOs so that we don't pass
wrong pointer to amdgpu_gtt_mgr_has_gart_addr() which assumes
ttm_resource argument to be TTM_PL_TT type BO's.

v3: remove extra braces.
v2: merge if-conditions.

Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210629114413.3371-1-nirmoy.das@amd.com