do_switch_ecc() calls fsmc_nand_switch_ecc(), which is a direct
function call into drivers/mtd/nand/fsmc_nand.c. However, this
function is not guarded by CONFIG_NAND_FSMC, which results to a build
failure if CONFIG_NAND_FSMC is disabled.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>