drm/nouveau/pmu: don't print reply values if exec is false

Currently the uninitialized values in the array reply are printed out
when exec is false and nvkm_pmu_send has not updated the array. Avoid
confusion by only dumping out these values if they have been actually
updated.

Detected by CoverityScan, CID#1271291 ("Uninitialized scaler variable")
Fixes: ebb58dc2 ("drm/nouveau/pmu: rename from pwr (no binary change)")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>