drm/bridge: ti-sn65dsi86: Remove __exit from GPIO sub-driver remove helper

The ti_sn_gpio_unregister() is not just called from the remove path
but also from the error handling of the init path. That means it can't
have the __exit annotation.

Fixes: bf73537f

 ("drm/bridge: ti-sn65dsi86: Break GPIO and MIPI-to-eDP bridge into sub-drivers")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210504073845.1.Ibf4194f4252846edaa0c6a6c7b86588f75ad5529@changeid