mmc: sdhci-msm: Set PWRSAVE bit to '0' during tuning

Set PWRSAVE bit to '0' before tuning, and set it to the initial value
after completion of tuning. Make sure that PWRSAVE bit is set to '0'
during tuning according to HPG.

Change-Id: Id32213f435b8b73cbaebff8b6068f37b93259925
Signed-off-by: Jun Li <liju@codeaurora.org>