mmc: core: prefer SDR50 mode over DDR50 for SD card

If Ultra High Speed SD card supports both SDR50 and DDR50 modes then
this change will give preference to SDR50 over DDR50 mode as it seems
to be more reliable for board designs. While we are doing this, this
change also fixes some indentation issues in the function we are have
modified.

Change-Id: Ifa075563ec41f43584d93f669caecbaed9369e24
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>