mtd: nand: fsmc: move fsmc_nand_data definition

This commit simply moves the "struct fsmc_nand_data" definition to be
towards the beginning of the file, with the other defines and type
definitions, instead of in the middle of the driver code. This is much
more consistent with what most Linux drivers do.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>