AP_Param: fixed PSTR() usage

libraries/AP_Param/AP_Param.cpp

@@ -1154,7 +1154,7 @@ void AP_Param::convert_old_parameter(const struct ConversionInfo *info)
     AP_Param *ap2;
     ap2 = find_P((const prog_char_t *)&info->new_name[0], &ptype);
     if (ap2 == NULL) {
-        hal.console->printf_P("Unknown conversion '%s'\n", info->new_name);
+        hal.console->printf_P(PSTR("Unknown conversion '%s'\n"), info->new_name);
         return;
     }
 
@@ -1184,7 +1184,7 @@ void AP_Param::convert_old_parameter(const struct ConversionInfo *info)
         }
     } else {
         // can't do vector<->scalar conversion, or different vector types
-        hal.console->printf_P("Bad conversion type '%s'\n", info->new_name);
+        hal.console->printf_P(PSTR("Bad conversion type '%s'\n"), info->new_name);
     }
 }
 #pragma GCC diagnostic pop