xfs: Fix a typo

s/strutures/structures/

Signed-off-by: Bhaskar Chowdhury <unixbhaskar@gmail.com>
Reviewed-by: Pavel Reichl <preichl@redhat.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>