AP_Math: do not use internal_error() on iofirmware

libraries/AP_Math/AP_Math.cpp

@@ -270,7 +270,9 @@ T constrain_value_line(const T amt, const T low, const T high, uint32_t line)
     // errors through any function that uses constrain_value(). The normal
     // float semantics already handle -Inf and +Inf
     if (isnan(amt)) {
+#if !defined(IOMCU_FW)
         AP::internalerror().error(AP_InternalError::error_t::constraining_nan, line);
+#endif
         return (low + high) / 2;
     }