mtd: rawnand: vf610: Remove unused function vf610_nfc_transfer_size()

commit ecc40b8d ("mtd: rawnand: vf610_nfc: remove old hooks")
left behind this, remove it.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200909134318.36340-1-yuehaibing@huawei.com