arm: mvebu: helios4: remove duplicate sdhci pins node

The same pinctrl node appears in the solidrun-microsom dtsi. Use that
instead.

Cc: Dennis Gilmore <dennis@ausil.us>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Reviewed-by: Dennis Gilmore <dennis@ausil.us>
Tested-by: Dennis Gilmore <dennis@ausil.us>
Signed-off-by: Stefan Roese <sr@denx.de>