xfs: fix xfs_iomap_eof_prealloc_initial_size type

Fix the return type of xfs_iomap_eof_prealloc_initial_size() to
xfs_fsblock_t to reflect the fact that the return value may be an
unsigned 64 bits if XFS_BIG_BLKNOS is defined.

Signed-off-by: Mark Tinguely <tinguely@sgi.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

(cherry picked from commit e8108cedb1)

fs/xfs/xfs_iomap.c

@@ -325,7 +325,7 @@ xfs_iomap_eof_want_preallocate(
  * rather than falling short due to things like stripe unit/width alignment of
  * real extents.
  */
-STATIC int
+STATIC xfs_fsblock_t
 xfs_iomap_eof_prealloc_initial_size(
 	struct xfs_mount	*mp,
 	struct xfs_inode	*ip,