mtd: nand: don't free the global data too early

The global data fsl_lbc_ctrl_dev->nand don't have to be freed in
fsl_elbc_chip_remove(). The right place to do that is in fsl_elbc_nand_remove()
if elbc_fcm_ctrl->counter is zero.

Signed-off-by: Liu Shuo <b35362@freescale.com>
Signed-off-by: Artem Bityutskiy <dedekind1@gmail.com>