mtd: rawnand: rockchip: Add missing title to a kernel doc comment

All fields of the nfc_cfg structure are documented but the name, which
leads to a W=1 warning. Add a title.

Fixes: 058e0e847d54 ("mtd: rawnand: rockchip: NFC driver for RK3308, RK2928 and others")
Signed-off-by: Miquel Raynal <[e-mail]>
Link: https://lore.kernel.org/linux-mtd/[e-mail]

drivers/mtd/nand/raw/rockchip-nand-controller.c

···
 };
 
 /**
+ * struct nfc_cfg: Rockchip NAND controller configuration
  * @type: NFC version
  * @ecc_strengths: ECC strengths
  * @ecc_cfgs: ECC config values