xfs: fix missing header includes

Some of the xfs source files are missing header includes, so add them
back.  Sparse complains about non-static functions that don't have a
forward declaration anywhere.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/libxfs/xfs_bit.c

@@ -5,6 +5,7 @@
  */
 #include "xfs.h"
 #include "xfs_log_format.h"
+#include "xfs_bit.h"
 
 /*
  * XFS bit manipulation routines, used in non-realtime code.