[XFS] kill calls to xfs_binval in the mount error path

xfs_binval aka xfs_flush_buftarg is the first thing done in
xfs_free_buftarg, so there is no need to have duplicated calls just before
xfs_free_buftarg in the mount failure path.

SGI-PV: 981951
SGI-Modid: xfs-linux-melb:xfs-kern:31197a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>