mtd: rawnand: gpmi: fix dst bit offset when extracting raw payload

Re-add the multiply by 8 to "step * eccsize" to correct the destination bit offset
when extracting the data payload in gpmi_ecc_read_page_raw().

Fixes: e5e5631c ("mtd: rawnand: gpmi: Use nand_extract_bits()")
Cc: stable@vger.kernel.org
Reported-by: Martin Hundebøll <martin@geanix.com>
Signed-off-by: Sean Nyekjaer <sean@geanix.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20201221100013.2715675-1-sean@geanix.com