mtd: rawnand: gpmi: Drop unnecessary restoring of previous chipselection

The i.MX23 specific option read code is called right after nand_scan. We
can rely on the NAND core having disabled the chipselect, so there's no
point in restoring the original chip select after NAND operations. Drop
it.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>