pata_octeon_cf: use devm_kzalloc() to allocate cf_port

As a nice side effect this fixes the cf_port leak on
dma_coerce_mask_and_coherent() or ata_host_activate()
failure.

Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: David Daney <david.daney@cavium.com>
Suggested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Tejun Heo <tj@kernel.org>