mp_image: call pl_color_space_infer in guess_csp

This will do a little bit more than only setting max_luma. Also will
fallback to bt.709/bt.1886, but that's fine. We would do it anyway
later.

If params goes through guess_csp, they shouldn't have "unknown" fields
anymore.

video/mp_image.c

@@ -1042,12 +1042,7 @@ void mp_image_params_guess_csp(struct mp_image_params *params)
 
     // If the signal peak is unknown, we're forced to pick the TRC's
     // nominal range as the signal peak to prevent clipping
-    pl_color_space_nominal_luma_ex(pl_nominal_luma_params(
-        .color      = &params->color,
-        .metadata   = PL_HDR_METADATA_HDR10,
-        .scaling    = PL_HDR_NITS,
-        .out_max    = &params->color.hdr.max_luma,
-    ));
+    pl_color_space_infer(&params->color);
 
     if (!pl_color_space_is_hdr(&params->color)) {
         // Some clips have leftover HDR metadata after conversion to SDR, so to