drm/msm: a6x: Rework qmp_get() error handling

Fix the following for qmp_get() errors:

1. Correctly handle probe defer for A6x GPUs
2. Ignore other errors because those are okay when GPU ACD is
not required. They are checked again during gpu acd probe.

Signed-off-by: Akhil P Oommen <quic_akhilpo@quicinc.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Tested-by: Maya Matuszczyk <maccraft123mc@gmail.com>
Tested-by: Anthony Ruhier <aruhier@mailbox.org>
Patchwork: https://patchwork.freedesktop.org/patch/649346/


Signed-off-by: Rob Clark <robdclark@chromium.org>