Fix build against linux >= 6.5.12

adapted from
https://github.com/asterisk/dahdi-linux/commit/a370c800599b8ee0ca1a843920452941e4d4dadc

see
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c4f135d643823a86
https://lore.kernel.org/all/49925af7-78a8-a3dd-bce6-cfc02e1a9236@I-love.SAKURA.ne.jp/T/#u

Change-Id: I992eccc503a19e348d3575147edcb9c2e78845eb
---
M include/dahdi/kernel.h
1 file changed, 26 insertions(+), 0 deletions(-)

diff --git a/include/dahdi/kernel.h b/include/dahdi/kernel.h
index 0a25854..b707753 100644
--- a/include/dahdi/kernel.h
+++ b/include/dahdi/kernel.h
@@ -1426,6 +1426,16 @@
 /*! Maximum audio mask */
 #define DAHDI_FORMAT_AUDIO_MASK	((1 << 16) - 1)
 
+#if LINUX_VERSION_CODE > KERNEL_VERSION(6,5,12)
+#undef flush_scheduled_work
+#define flush_scheduled_work()				\
+({							\
+	if (0)						\
+		__warn_flushing_systemwide_wq();	\
+	__flush_workqueue(system_wq);			\
+})
+#endif
+
 #if LINUX_VERSION_CODE < KERNEL_VERSION(4, 15, 0)
 
 #ifndef TIMER_DATA_TYPE

