mmc: sdhci: Fix HISPD bit handling for MMC HS 52MHz mode

Set High Speed Enable bit for MMC High Speed (52MHz) mode.

Fixes: f12341a9 ("mmc: sdhci: Fix HISPD bit handling")
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>