ARM: iop: don't use using 64-bit DMA masks

clang warns about statically defined DMA masks from the DMA_BIT_MASK
macro with length 64:

 arch/arm/mach-iop13xx/setup.c:303:35: error: shift count >= width of type [-Werror,-Wshift-count-overflow]
 static u64 iop13xx_adma_dmamask = DMA_BIT_MASK(64);
                                  ^~~~~~~~~~~~~~~~
 include/linux/dma-mapping.h:141:54: note: expanded from macro 'DMA_BIT_MASK'
 #define DMA_BIT_MASK(n) (((n) == 64) ? ~0ULL : ((1ULL<<(n))-1))
                                                      ^ ~~~

The ones in iop shouldn't really be 64 bit masks, so changing them
to what the driver can support avoids the warning.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Olof Johansson <olof@lixom.net>