motech-lps-30x: Make serial write call block.

This call was previously explicitly nonblocking, but has no partial write
handling. It sends a short packet so should be OK to block, most likely the
output buffer will be empty anyway.

src/hardware/motech-lps-30x/api.c

@@ -146,7 +146,7 @@ SR_PRIV int lps_send_va(struct sr_serial_dev_inst *serial, const char* fmt, va_l
 
 	sr_spew("lps_send_va: \"%s\"", buf);
 
-	retc = serial_write_nonblocking(serial, buf, strlen(buf));
+	retc = serial_write_blocking(serial, buf, strlen(buf));
 
 	if (retc < 0)
 		return SR_ERR;