drm/msm: Quiet error during failure in optional resource mappings.

We don't expect to find vbif_nrt or regdma on sdm845, but were clogging
up dmesg with errors about it.

Signed-off-by: Eric Anholt <eric@anholt.net>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Rob Clark <robdclark@chromium.org>