mmc: sdhci-of-dwcmshc: Prevent illegal clock reduction in HS200/HS400 mode

mmc: sdhci-of-dwcmshc: Prevent illegal clock reduction in HS200/HS400 mode

commit 3009738a855cf938bbfc9078bec725031ae623a4 upstream.

When operating in HS200 or HS400 timing modes, reducing the clock frequency
below 52MHz will lead to link broken as the Rockchip DWC MSHC controller
requires maintaining a minimum clock of 52MHz in these modes.

Add a check to prevent illegal clock reduction through debugfs:

root@debian:/# echo 50000000 > /sys/kernel/debug/mmc0/clock
root@debian:/# [   30.090146] mmc0: running CQE recovery
mmc0: cqhci: Failed to halt
mmc0: cqhci: spurious TCN for tag 0
WARNING: drivers/mmc/host/cqhci-core.c:797 at cqhci_irq+0x254/0x818, CPU#1: kworker/1:0H/24
Modules linked in:
CPU: 1 UID: 0 PID: 24 Comm: kworker/1:0H Not tainted 6.19.0-rc1-00001-g09db0998649d-dirty #204 PREEMPT
Hardware name: Rockchip RK3588 EVB1 V10 Board (DT)
Workqueue: kblockd blk_mq_run_work_fn
pstate: 604000c9 (nZCv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : cqhci_irq+0x254/0x818
lr : cqhci_irq+0x254/0x818
...

Fixes: c6f361cba51c ("mmc: sdhci-of-dwcmshc: add support for rk3588")
Cc: Sebastian Reichel <sebastian.reichel@collabora.com>
Cc: Yifeng Zhao <yifeng.zhao@rock-chips.com>
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>