mtd: mxc_nand: remove duplicated ecc_stats counting

The ecc_stats.corrected count variable will already be incremented in
the above framework-layer just after this callback.

Cc: stable@vger.kernel.org # 2.6.36+
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>