drm/msm/a6xx: Fix unknown speedbin case

drm/msm/a6xx: Fix unknown speedbin case

When opp-supported-hw is present under an OPP node, but no form of
opp_set_supported_hw() has been called, that OPP is ignored by the API
and marked as unsupported.

Before Commit c928a05e4415 ("drm/msm/adreno: Move speedbin mapping to
device table"), an unknown speedbin would result in marking all OPPs
as available, but it's better to avoid potentially overclocking the
silicon - the GMU will simply refuse to power up the chip.

Currently, the Adreno speedbin code does just that (AND returns an
invalid error, (int)UINT_MAX). Fix that by defaulting to speedbin 0
(which is conveniently always bound to fuseval == 0).

Fixes: c928a05e4415 ("drm/msm/adreno: Move speedbin mapping to device table")
Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/559604/
Signed-off-by: Rob Clark <robdclark@chromium.org>