drm/i915/display: remove useless use of inline

skl_scaler_get_filter_select() isn't static and can't be inline.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210113143726.19701-1-jani.nikula@intel.com