Fix compiler warning: unused variable when building with DEBUG

clients/keyboard.c: In function 'dbg':
clients/keyboard.c:276:6: warning: variable 'l' set but not used [-Wunused-but-set-variable]
  int l;

Signed-off-by: Marius Vlad <marius.vlad0@gmail.com>

clients/keyboard.c

@@ -273,11 +273,10 @@ static void __attribute__ ((format (printf, 1, 2)))
 dbg(const char *fmt, ...)
 {
 #ifdef DEBUG
-	int l;
 	va_list argp;
 
 	va_start(argp, fmt);
-	l = vfprintf(stderr, fmt, argp);
+	vfprintf(stderr, fmt, argp);
 	va_end(argp);
 #endif
 }