linux/generic/hack-5.15: add missing patch headers

This patches does not have a valid patch headers and does not apply on
an external git tree with 'git am'. To fix this add the missing headers.

Signed-off-by: Florian Eckert <fe@dev.tdt.de>

target/linux/generic/hack-5.15/920-device_tree_cmdline.patch

@@ -1,6 +1,17 @@
+From e08bcbbaa52fcc41f02743fd2e62a33255ce52da Mon Sep 17 00:00:00 2001
+From: OpenWrt community <openwrt-devel@lists.openwrt.org>
+Date: Wed, 13 Jul 2022 13:52:28 +0200
+Subject: [PATCH] of/ftd: add device tree cmdline
+
+---
+ drivers/of/fdt.c | 3 +++
+ 1 file changed, 3 insertions(+)
+
+diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
+index 59a7a9ee58ef..3b0b62b410dd 100644
 --- a/drivers/of/fdt.c
 +++ b/drivers/of/fdt.c
-@@ -1158,6 +1158,9 @@ int __init early_init_dt_scan_chosen(uns
+@@ -1158,6 +1158,9 @@ int __init early_init_dt_scan_chosen(unsigned long node, const char *uname,
  	p = of_get_flat_dt_prop(node, "bootargs", &l);
  	if (p != NULL && l > 0)
  		strlcpy(data, p, min(l, COMMAND_LINE_SIZE));
@@ -10,3 +21,5 @@
  
  	/*
  	 * CONFIG_CMDLINE is meant to be a default in case nothing else
+-- 
+