libtracefs: Fix the /dev/null redirection compatibility in Makefile

"&> /dev/null" is bash shell syntax, use more compatible syntax to handle
shell null redirection.

/bin/sh: 1: /root/linux/libtracefs/test: not found
In file included from /root/linux/libtracefs/test.c:1:
/usr/local/include/tracefs/tracefs.h:11:10: fatal error: event-parse.h: No such file or directory
   11 | #include <event-parse.h>
      |          ^~~~~~~~~~~~~~~
compilation terminated.

Link: https://lore.kernel.org/20250523174850.471638-1-haiyuewa@163.com
Signed-off-by: Haiyue Wang <haiyuewa@163.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>