mtd: Blackfin NFC: wait for the ECC reset to finish

When resetting the ECC registers/counters, the bit will automatically
clear itself once the reset has actually finished.  So make sure we
wait for that to occur before doing anything else rather than assuming
everything is peachy and proceeding with stale ECC values.

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>