mtd: atmel_nand: fix support for CPUs that do not support DMA access
use_dma was always "1" even if the CPU does not support DMA
Tested on AT91SAM9261EK by Jean-Christophe PLAGNIOL-VILLARD
Reported-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Hong Xu <hong.xu@atmel.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>