mmc: sdhci-st: correct name of sd-uhs-sdr50 property

Correct what appears to be a typo in the name of the sd-uhs-sdr50.

Also fix mixed tab/space indentation.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>