mmc: sdhci-msm: Clear tuning done flag while hs400 tuning

Clear tuning_done flag while executing tuning to ensure vendor
specific HS400 settings are applied properly when the controller
is re-initialized in HS400 mode.

Without this, re-initialization of the qcom SDHC in HS400 mode fails
while resuming the driver from runtime-suspend or system-suspend.

Fixes: ff06ce41

 ("mmc: sdhci-msm: Add HS400 platform support")
Cc: stable@vger.kernel.org
Signed-off-by: Veerabhadrarao Badiganti <vbadigan@codeaurora.org>
Link: https://lore.kernel.org/r/1590678838-18099-1-git-send-email-vbadigan@codeaurora.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>