zynq: mtd: nand: remove superfluous if

This sort of code does not make much sense:

    if (ondie_ecc_enabled) {
        if (ondie_ecc_enabled) {

Remove the inner if.

The problem was indicated by cppcheck.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>