mtd: Blackfin NFC: fix typo for read/write delay setup

We used the platform rd_dly field when we meant to use the wr_dly field.

Signed-off-by: Barry Song <barry.song@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>