blk-iolatency: #include "blk.h"

This patch avoids that the following warning is reported when building
with W=1:

block/blk-iolatency.c:734:5: warning: no previous prototype for 'blk_iolatency_init' [-Wmissing-prototypes]

Cc: Josef Bacik <jbacik@fb.com>
Fixes: d7067512 ("block: introduce blk-iolatency io controller") # v4.19
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-iolatency.c

@@ -75,6 +75,7 @@
 #include <linux/blk-mq.h>
 #include "blk-rq-qos.h"
 #include "blk-stat.h"
+#include "blk.h"
 
 #define DEFAULT_SCALE_COOKIE 1000000U