ARM: at91/dt: sama5d2: Fix the warning from dtc

Fix the warning from dtc like,
---8<----
Warning (unit_address_vs_reg): Node /ahb/apb/pmc@f0014000/periph64ck/sdmmc0_hclk has a reg or ranges property, but no unit name
--->8----

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Acked-by: Stephen Warren <swarren@nvidia.com>