mtd: spinand: toshiba: Add comment about Kioxia ID

Add a comment above NAND_MFR_TOSHIBA and SPINAND_MFR_TOSHIBA definitions
that Toshiba and Kioxia ID are the same.
Since its independence from Toshiba Group, Toshiba memory Co has become
Kioxia Co.

Signed-off-by: Yoshio Furuyama <ytc-mb-yfuruyama7@kioxia.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/1581051561-7302-1-git-send-email-ytc-mb-yfuruyama7@kioxia.com