pstore: inode: Convert kfree() usage to __free(kfree)

Mostly as an example to myself, replace a simple allocation pattern with
the automatic kfree cleanup features now exposed by cleanup.h.

Cc: Guilherme G. Piccoli <gpiccoli@igalia.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc:  <linux-hardening@vger.kernel.org>
Link: https://lore.kernel.org/r/20231205182622.1329923-1-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>

Author: kees

fs/pstore/inode.c

@@ -23,6 +23,7 @@
 #include <linux/pstore.h>
 #include <linux/slab.h>
 #include <linux/uaccess.h>
+#include <linux/cleanup.h>
 
 #include "internal.h"
 
@@ -64,21 +65,18 @@ static void free_pstore_private(struct pstore_private *private)
 static void *pstore_ftrace_seq_start(struct seq_file *s, loff_t *pos)
 {
 	struct pstore_private *ps = s->private;
-	struct pstore_ftrace_seq_data *data;
+	struct pstore_ftrace_seq_data *data __free(kfree) = NULL;
 
 	data = kzalloc(sizeof(*data), GFP_KERNEL);
 	if (!data)
 		return NULL;
 
 	data->off = ps->total_size % REC_SIZE;
 	data->off += *pos * REC_SIZE;
-	if (data->off + REC_SIZE > ps->total_size) {
-		kfree(data);
+	if (data->off + REC_SIZE > ps->total_size)
 		return NULL;
-	}
-
-	return data;
 
+	return_ptr(data);
 }
 
 static void pstore_ftrace_seq_stop(struct seq_file *s, void *v)