helpers: new macro to CLAMP high threshold only

Useful when clamping a unsigned integer with low threshold set to 0,
which would give us compiler warnings with -Wtype-limits when using
CLAMP(), e.g.:

  via/mm-broadband-modem-via.c: In function ‘handle_evdo_quality_change’:
  /usr/include/glib-2.0/glib/gmacros.h:811:63: error: comparison of unsigned expression < 0 is always false [-Werror=type-limits]
    811 | #define CLAMP(x, low, high)  (((x) > (high)) ? (high) : (((x) < (low)) ? (low) : (x)))
        |                                                               ^
  via/mm-broadband-modem-via.c:284:19: note: in expansion of macro ‘CLAMP’
    284 |         quality = CLAMP (quality, 0, 100);
        |                   ^~~~~

src/mm-broadband-modem-mbim.c

@@ -1674,12 +1674,8 @@ signal_state_query_ready (MbimDevice *device,
             NULL, /* rssi_threshold */
             NULL, /* error_rate_threshold */
             &error)) {
-        guint32 quality;
-
         /* Normalize the quality. 99 means unknown, we default it to 0 */
-        quality = CLAMP (rssi == 99 ? 0 : (gint)rssi, 0, 31) * 100 / 31;
-
-        g_task_return_int (task, quality);
+        g_task_return_int (task, MM_CLAMP_HIGH (rssi == 99 ? 0 : rssi, 31) * 100 / 31);
     } else
         g_task_return_error (task, error);
 
@@ -2920,7 +2916,7 @@ basic_connect_notification_signal_state (MMBroadbandModemMbim *self,
         guint32 quality;
 
         /* Normalize the quality. 99 means unknown, we default it to 0 */
-        quality = CLAMP (rssi == 99 ? 0 : (gint)rssi, 0, 31) * 100 / 31;
+        quality = MM_CLAMP_HIGH (rssi == 99 ? 0 : rssi, 31) * 100 / 31;
 
         mm_dbg ("Signal state indication: %u --> %u%%", rssi, quality);
         mm_iface_modem_update_signal_quality (MM_IFACE_MODEM (self), quality);

src/mm-modem-helpers.h

@@ -504,4 +504,10 @@ gboolean mm_parse_supl_address (const gchar  *supl,
                                 guint16      *out_port,
                                 GError      **error);
 
+/*****************************************************************************/
+
+/* Useful when clamp-ing an unsigned integer with implicit low limit set to 0,
+ * and in order to avoid -Wtype-limits warnings. */
+#define MM_CLAMP_HIGH(x, high) (((x) > (high)) ? (high) : (x))
+
 #endif  /* MM_MODEM_HELPERS_H */