iwlwifi: mvm: catch underflow error earlier

My static checker complains that we don't check for underflows in
iwl_dbgfs_fw_dbg_conf_write().  This is harmless because we have a
sanity check in iwl_mvm_start_fw_dbg_conf(), but we may as well make
this unsigned and silence the underflow warning.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>

drivers/net/wireless/iwlwifi/mvm/debugfs.c

@@ -949,9 +949,10 @@ static ssize_t iwl_dbgfs_fw_dbg_conf_write(struct iwl_mvm *mvm,
 					   char *buf, size_t count,
 					   loff_t *ppos)
 {
-	int ret, conf_id;
+	unsigned int conf_id;
+	int ret;
 
-	ret = kstrtoint(buf, 0, &conf_id);
+	ret = kstrtouint(buf, 0, &conf_id);
 	if (ret)
 		return ret;