frame_fifo: add missing declaration

/build/drivers/dahdi/trunkdev/frame_fifo.c:32:6: error: no previous prototype for 'fifo_dump' [-Werror=missing-prototypes]
   32 | void fifo_dump(struct frame_fifo *fifo)
      |      ^~~~~~~~~
cc1: all warnings being treated as errors

Change-Id: I02eccb9c404157352d6c317b02d742b90c229deb
---
M drivers/dahdi/trunkdev/frame_fifo.h
1 file changed, 17 insertions(+), 0 deletions(-)

diff --git a/drivers/dahdi/trunkdev/frame_fifo.h b/drivers/dahdi/trunkdev/frame_fifo.h
index b07cddc..daf7b01 100644
--- a/drivers/dahdi/trunkdev/frame_fifo.h
+++ b/drivers/dahdi/trunkdev/frame_fifo.h
@@ -56,3 +56,6 @@
 
 /* pull multiple frames out of the FIFO */
 int frame_fifo_out_multi(struct frame_fifo *fifo, uint8_t *out, size_t count);
+
+/* dump FIFO state to kernel log */
+void fifo_dump(struct frame_fifo *fifo);

