mmc: atmel-mci: change atmci_readl and atmci_writel macros

Change atmci_readl and atmci_writel macros: remove string concatenation.
We can use these macros with registers which are not prefixed by ATMCI_.
This is the case if we want to write PDC registers which are common to
several devices so they are not prefixed with ATMCI_.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Chris Ball <cjb@laptop.org>