dma-trace.c: lower log level of dropped logs and stop recursion

Dropping logs is bad but it should not be fatal in itself.

This ERROR is one of the last remaining errors in stable-v2.2, see
thesofproject/sof-test#1075 (comment)

Also switch to the "etrace": drop the dubious recursion and stop using
the DMA trace when it's already saturated.

Disclaimer: this was (successfully) tested only on stable-v2.2, see #9036

Signed-off-by: Marc Herbert <marc.herbert@intel.com>
(cherry picked from commit bb31696)

src/trace/dma-trace.c

@@ -645,15 +645,9 @@ static void dtrace_add_event(const char *e, uint32_t length)
 			uint32_t tmp_dropped_entries =
 				trace_data->dropped_entries;
 			trace_data->dropped_entries = 0;
-			/*
-			 * this trace_error invocation causes recursion,
-			 * so after it we have to recalculate margin and
-			 * overflow
-			 */
-			tr_err(&dt_tr, "dtrace_add_event(): number of dropped logs = %u",
-			       tmp_dropped_entries);
-			margin = dtrace_calc_buf_margin(buffer);
-			overflow = dtrace_calc_buf_overflow(buffer, length);
+			mtrace_printf(LOG_LEVEL_WARNING,
+				      "dtrace_add_event(): number of dropped logs = %u",
+				      tmp_dropped_entries);
 		}
 	}