nandtest: print number of bits corrected during test

nandtest: print number of bits corrected during test

The nandtest program monitors the corrected ecc stat to determine if an
ECC correction has taken place during the last write-read. If so, it
prints "ECC corrected".

The mtd subsytem will store the number of bits corrected in the corrected
ecc stat so update the nandtest output to print also the number of bits
corrected when performing the test.

Signed-off-by: Ben Gardiner <bengardiner@nanometrics.ca>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@intel.com>