dm stripe: fix potential for leak in stripe_ctr error path

Fix a potential struct stripe_c leak that would occur if the
chunk_size exceeded the maximum allowed by dm_set_target_max_io_len
(UINT_MAX).  However, in practice there is no possibility of this
occuring given that chunk_size is of type uint32_t.  But it is good to
fix this to future-proof in case dm_set_target_max_io_len's
implementation were to change.

Signed-off-by: Pavitra Kumar <pavitrak@nvidia.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>