serial-dmm: Increase timeout when scanning for DMMs.

We have to wait a bit longer than 1s for a valid DMM packet to arrive,
since for various DMMs some modes (Hz/% for example) the packets will
arrive a lot less often than in other modes. If the waiting period is
too short detection of the DMM will fail.

hardware/serial-dmm/api.c

@@ -329,7 +329,7 @@ static GSList *sdmm_scan(const char *conn, const char *serialcomm, int dmm)
 	/* Let's get a bit of data and see if we can find a packet. */
 	len = sizeof(buf);
 	ret = serial_stream_detect(serial, buf, &len, dmms[dmm].packet_size,
-				   dmms[dmm].packet_valid, 1000,
+				   dmms[dmm].packet_valid, 3000,
 				   dmms[dmm].baudrate);
 	if (ret != SR_OK)
 		goto scan_cleanup;