iwlwifi: pcie: make FH debugfs file code easier to understand

The code seems fine, as buf won't be assigned when an error
is returned, but checking for the error first is easier to
understand.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>

drivers/net/wireless/iwlwifi/pcie/trans.c

@@ -1434,16 +1434,15 @@ static ssize_t iwl_dbgfs_fh_reg_read(struct file *file,
 {
 	struct iwl_trans *trans = file->private_data;
 	char *buf = NULL;
-	int pos = 0;
-	ssize_t ret = -EFAULT;
-
-	ret = pos = iwl_dump_fh(trans, &buf);
-	if (buf) {
-		ret = simple_read_from_buffer(user_buf,
-					      count, ppos, buf, pos);
-		kfree(buf);
-	}
+	ssize_t ret;
 
+	ret = iwl_dump_fh(trans, &buf);
+	if (ret < 0)
+		return ret;
+	if (!buf)
+		return -EINVAL;
+	ret = simple_read_from_buffer(user_buf, count, ppos, buf, ret);
+	kfree(buf);
 	return ret;
 }