drm/bridge: ti-sn65dsi86: annotate ti_sn_pwm_pin_{request, release} with __maybe_unused

Building with clang, W=1, CONFIG_PM=n and CONFIG_OF_GPIO=n leads to
warning about unused ti_sn_pwm_pin_request() and
ti_sn_pwm_pin_release(). Fix by annotating them with __maybe_unused.

See also commit 6863f564 ("kbuild: allow Clang to find unused static
inline functions for W=1 build").

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/136ecd978aedd7df39d1b1c37b70596027ff0a3e.1725962479.git.jani.nikula@intel.com