platform/x86: dell_rbu: avoid uninit value usage in packet_size_write()

Ensure the temp value has been properly parsed from the user-provided
buffer and initialized to be used in later operations.  While at it,
prefer a convenient kstrtoul() helper.

Found by Linux Verification Center (linuxtesting.org) with Svace static
analysis tool.

Fixes: ad6ce87 ("[PATCH] dell_rbu: changes in packet update mechanism")
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Link: https://patch.msgid.link/20260403134240.604837-1-pchelkin@ispras.ru
[ij: add include]
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

Author: pchelkin91

drivers/platform/x86/dell/dell_rbu.c

@@ -30,6 +30,7 @@
 #define pr_fmt(fmt)	KBUILD_MODNAME ": " fmt
 
 #include <linux/init.h>
+#include <linux/kstrtox.h>
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/string.h>
@@ -619,9 +620,12 @@ static ssize_t packet_size_write(struct file *filp, struct kobject *kobj,
 				 char *buffer, loff_t pos, size_t count)
 {
 	unsigned long temp;
+
+	if (kstrtoul(buffer, 10, &temp))
+		return -EINVAL;
+
 	spin_lock(&rbu_data.lock);
 	packet_empty_list();
-	sscanf(buffer, "%lu", &temp);
 	if (temp < 0xffffffff)
 		rbu_data.packetsize = temp;