mtd: rawnand: fsmc: Fix the fsmc_nand_data kernel-doc

The kernel-doc describing struct fsmc_nand_data is not in sync with
the struct itself. Add missing entries and drop invalid ones.

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>