Use an unsigned integer for storing the key code.

It seems Clang breaks when checking for SPCLKEY, which is now
0x80000000. Using an unsigned integer fixes this. This is also
consistent with other pieces of kbd/syscons code, because these also use
u_int.

Submitted by:	rdivacky

sys/dev/kbd/kbd.c

@@ -728,7 +728,7 @@ genkbd_event(keyboard_t *kbd, int event, void *arg)
 	size_t len;
 	u_char *cp;
 	int mode;
-	int c;
+	u_int c;
 
 	/* assert(KBD_IS_VALID(kbd)) */
 	sc = (genkbd_softc_t *)arg;