mtd: rawnand: gpmi: Remove explicit default gpmi clock setting for i.MX6

There is no need to explicitly set the default gpmi clock rate during
boot for the i.MX 6 since this is done during nand_detect anyway.

Signed-off-by: Stefan Riedmueller <s.riedmueller@phytec.de>
Cc: stable@vger.kernel.org
Acked-by: Han Xu <han.xu@nxp.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20211102202022.15551-1-ceggers@arri.de