mmc: renesas_sdhi: drop local flag for tuning

The MMC core has now a generic check if some tuning is in progress. Its
protected area is a bit larger than the custom one in this driver but we
concluded that this works equally well for the intended case. So, drop
the local flag and switch to the generic one.

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/20200922172253.4458-1-wsa@kernel.org


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