[][openwrt][common][bsp][Add ignore item of checkpatch]

[Description]
Add --ignore PREFER_PRINTF to .checkpatch.conf

[Release-log]
N/A

Change-Id: Idab584be8678f648633b29e55db0cc90cfe74193
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/9407395
diff --git a/.checkpatch.conf b/.checkpatch.conf
index 45bf9d0..e5d05b7 100644
--- a/.checkpatch.conf
+++ b/.checkpatch.conf
@@ -9,3 +9,5 @@
 --ignore SPDX_LICENSE_TAG
 --ignore CONST_STRUCT
 --ignore MACRO_WITH_FLOW_CONTROL
+--ignore PREFER_PRINTF
+