mmc: core: when downgrading HS400, callback into drivers earlier

The driver specific downgrade function makes more sense if we run it
before we set the timing to something lower, not after. Otherwise some
non-HS400 communication has already happened.

No need to convert users. There is only one currently which needs this
change in a following patch.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/20200901150250.26236-2-wsa+renesas@sang-engineering.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>