sunxi-mmc: don't double clock for new mode unconditionally

Comment in Linux driver says that clock needs to be doubled only
if we use DDR modes, moreover divider has to be set accordingly.

U-boot driver doesn't declare support for any DDR modes and doesn't
set internal clock divider in CLKCR, so it doubles clock
unconditionally when new mode is used.

Some cards can't handle that and as result SPL fails to load u-boot.

Fixes: de9b1771

 ("mmc: sunxi: Support new mode")
Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>
Tested-by: Jagan Teki <jagan@amarulasolutions.com> # Amarula A64-Relic