Lib: Add to dai-legacy.h struct copier_gain_params for testbench

The new copier gain feature needs this structure. The added
member is copied directly from dai-zephyr.h. Testbench IPC4
is using legacy DAI definitions instead of Zephyr DAI to avoid
to include a lot of difficult dependencies. Build of testbench
fails if dai-legacy.h does not contain this.

Signed-off-by: Seppo Ingalsuo <seppo.ingalsuo@linux.intel.com>

src/include/sof/lib/dai-legacy.h

@@ -210,6 +210,9 @@ struct dai_data {
 
 	/* llp slot info in memory windows */
 	struct llp_slot_info slot_info;
+
+	/* Copier gain params */
+	struct copier_gain_params *gain_data;
 };
 
 struct dai {