mmc: sdhci-msm: fix pwrsave bit handling

SDCC controller provides the PWRSAVE control bit to automatically
disable the clock to card when there is no activity with card.
During the SDCC DLL tuning, PWRSAVE is disabled to make sure that clock
is always running but once the DLL tuning is completed, currently we
enable the PWRSAVE unconditionally irrespective of its previous state.

This change ensures that we always check if the previous state of pwrsave
before really enabling it.

Change-Id: I464ab1e0db41af50550bb5a9ea9b909ee0d27dd9
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>