[XFS] Check return value of xfs_buf_get_noaddr()

We check the return value of all other calls to xfs_buf_get_noaddr().
Make sense to do it here too.

Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Reviewed-by: Christoph Hellwig <hch@infradead.org>
Reviewed-by: Eric Sandeen <sandeen@sandeen.net>