dt-bindings: mmc: cdns: remove Piotr Sroka as a maintainer

Mails to Piotr bounce with a :550 5.1.1 User Unknown and the last
mention of him on lore is the orphaning of Cadence NFC drivers.
Remove him from the binding too.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20220811204024.182453-1-mail@conchuod.ie


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>