radeonsi/vcn: Don't hang GPU when using DCC surface as encoder input

Using DCC surface as encoder input will result in corrupted image in the
video, but early returning here will instead hang GPU.
Replace return with assert.

Reviewed-by: Leo Liu <leo.liu@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25259>

src/gallium/drivers/radeonsi/radeon_vcn_enc_1_2.c

@@ -1222,7 +1222,7 @@ static void radeon_enc_encode_params(struct radeon_encoder *enc)
 
    if (enc->luma->meta_offset) {
       RVID_ERR("DCC surfaces not supported.\n");
-      return;
+      assert(false);
    }
 
    enc->enc_pic.enc_params.allowed_max_bitstream_size = enc->bs_size;

src/gallium/drivers/radeonsi/radeon_vcn_enc_4_0.c

@@ -887,7 +887,7 @@ static void radeon_enc_av1_encode_params(struct radeon_encoder *enc)
 
    if (enc->luma->meta_offset) {
       RVID_ERR("DCC surfaces not supported.\n");
-      return;
+      assert(false);
    }
 
    enc->enc_pic.enc_params.allowed_max_bitstream_size = enc->bs_size;