wminput/plugins/led/led.c: fix build with gcc >= 14

Fix the following build failure with gcc >= 14:

led.c: In function 'wmplugin_exec':
led.c:86:42: error: assignment to 'struct cwiid_btn_message *' from incompatible pointer type 'struct cwiid_btn_mesg *' [-Wincompatible-pointer-types]
   86 |                                 btn_mesg = &mesg[i].btn_mesg;
      |                                          ^

Fixes:
 - http://autobuild.buildroot.org/results/a3bde74ff2137d088f4261e62930859bfe460cb9

Signed-off-by: Fabrice Fontaine <[email protected]>

wminput/plugins/led/led.c

@@ -83,7 +83,7 @@ struct wmplugin_data *wmplugin_exec(int mesg_count, union cwiid_mesg mesg[])
 		btn_mesg = NULL;
 		for (i=0; i < mesg_count; i++) {
 			if (mesg[i].type == CWIID_MESG_BTN) {
-				btn_mesg = &mesg[i].btn_mesg;
+				btn_mesg = (struct cwiid_btn_message *) &mesg[i].btn_mesg;
 				button = mesg[i].btn_mesg.buttons;
 			}
 		}