mtd: rawnand: gpmi: fix controller timings setting

[ Upstream commit 2970bf5a32f079e1e9197411db4fe9faccb1503a ]

Set the controller registers according to the real clock rate. The
controller registers configuration (setup, hold, timeout, ... cycles)
depends on the clock rate of the GPMI. Using the real rate instead of
the ideal one, avoids that this inaccuracy (required_rate - real_rate)
affects the registers setting.

This patch has been tested on two custom boards with i.MX28 and i.MX6
SOCs:
- i.MX28:
  required rate 100MHz, real rate 99.3MHz
- i.MX6
  required rate 100MHz, real rate 99MHz

Fixes: b1206122 ("mtd: rawnand: gpmi: use core timings instead of an empirical derivation")
Co-developed-by: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Tested-by: Sascha Hauer <s.hauer@pengutronix.de>
Reviewed-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220118095434.35081-3-dario.binacchi@amarulasolutions.com


Signed-off-by: Sasha Levin <sashal@kernel.org>