misc: Avoid UTF-8 in error messages

While most developers are now using UTF-8 environments, it's
harder to guarantee that error messages will be output to
a multibyte locale. Rather than risking error messages that
get corrupted into mojibake when the user runs qemu in a
non-multibyte locale, let's stick to straight ASCII error
messages, rather than assuming that our use of UTF-8 in source
code string constants will work unchanged in other locales.

Found with:
$ LC_ALL=C git grep -l $'".*[\x80-\xff].*"' origin -- '**/*.[ch]' | cat
origin:hw/misc/tmp105.c
origin:hw/misc/tmp421.c
Reported-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NJohn Snow <jsnow@redhat.com>
Reviewed-by: NThomas Huth <thuth@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Message-Id: <20181120203628.2367003-1-eblake@redhat.com>
[lv: added command line to find non ASCII characters]
Signed-off-by: NLaurent Vivier <laurent@vivier.eu>

hw/misc/tmp105.c

@@ -79,7 +79,7 @@ static void tmp105_set_temperature(Object *obj, Visitor *v, const char *name,
         return;
     }
     if (temp >= 128000 || temp < -128000) {
-        error_setg(errp, "value %" PRId64 ".%03" PRIu64 " °C is out of range",
+        error_setg(errp, "value %" PRId64 ".%03" PRIu64 " C is out of range",
                    temp / 1000, temp % 1000);
         return;
     }

hw/misc/tmp421.c

@@ -153,7 +153,7 @@ static void tmp421_set_temperature(Object *obj, Visitor *v, const char *name,
     }
 
     if (temp >= maxs[ext_range] || temp < mins[ext_range]) {
-        error_setg(errp, "value %" PRId64 ".%03" PRIu64 " °C is out of range",
+        error_setg(errp, "value %" PRId64 ".%03" PRIu64 " C is out of range",
                    temp / 1000, temp % 1000);
         return;
     }