drm/panel: ilitek-ili9881c: do not fail probe if iovcc is absent

drm/panel: ilitek-ili9881c: do not fail probe if iovcc is absent

Commit 4c95b2b7d49e ("drm/panel: ilitek-ili9881c: support Waveshare
7.0" DSI panel") adds an additional iovcc regulator that other
Ilitek ili9881c based panels apparently do not have or need.

The commit goes out of its way to make usage of this new regulator
optional, dutifully testing if the field in `struct ili9881c` is NULL
before touching the new regulator. However, in the probe function,
it unconditionally fails if devm_regulator_get_optional returns an
error.

devm_regulator_get_optional() returns -ENODEV if the regulator is
missing, causing probe to fail for other panels that do not have
an iovcc-supply set in the device tree.

Fixes: 4c95b2b7d49e ("drm/panel: ilitek-ili9881c: support Waveshare 7.0" DSI panel")
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patch.msgid.link/20260713082213.75759-1-david.oberhollenzer@sigma-star.at