Add include <blkdev.h>.

Fixes: Error: implicit declaration of function ‘blkdev_put’

Previously this was an `extern` in <fs.h> and included implicitly,
hence the need to hard include it now.

Signed-off-by: Auke Kok <auke.kok@versity.com>

kmod/src/super.c

@@ -13,6 +13,7 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/fs.h>
+#include <linux/blkdev.h>
 #include <linux/slab.h>
 #include <linux/pagemap.h>
 #include <linux/magic.h>