ftrace: Initialize variables for ftrace_startup/shutdown_subops()

The reworking to fix and simplify the ftrace_startup_subops() and the
ftrace_shutdown_subops() made it possible for the filter_hash and
notrace_hash variables to be used uninitialized in a way that the compiler
did not catch it.

Initialize both filter_hash and notrace_hash to the EMPTY_HASH as that is
what they should be if they never are used.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/20250417104017.3aea66c2@gandalf.local.home
Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Fixes: 0ae6b8c ("ftrace: Fix accounting of subop hashes")
Closes: https://lore.kernel.org/all/1db64a42-626d-4b3a-be08-c65e47333ce2@linux.ibm.com/
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

kernel/trace/ftrace.c

@@ -3490,8 +3490,8 @@ static int add_next_hash(struct ftrace_hash **filter_hash, struct ftrace_hash **
  */
 int ftrace_startup_subops(struct ftrace_ops *ops, struct ftrace_ops *subops, int command)
 {
-	struct ftrace_hash *filter_hash;
-	struct ftrace_hash *notrace_hash;
+	struct ftrace_hash *filter_hash = EMPTY_HASH;
+	struct ftrace_hash *notrace_hash = EMPTY_HASH;
 	struct ftrace_hash *save_filter_hash;
 	struct ftrace_hash *save_notrace_hash;
 	int ret;
@@ -3625,8 +3625,8 @@ static int rebuild_hashes(struct ftrace_hash **filter_hash, struct ftrace_hash *
  */
 int ftrace_shutdown_subops(struct ftrace_ops *ops, struct ftrace_ops *subops, int command)
 {
-	struct ftrace_hash *filter_hash;
-	struct ftrace_hash *notrace_hash;
+	struct ftrace_hash *filter_hash = EMPTY_HASH;
+	struct ftrace_hash *notrace_hash = EMPTY_HASH;
 	int ret;
 
 	if (unlikely(ftrace_disabled))