mtd: atmel_nand: remove redundant dev_err call

There is a error message within devm_ioremap_resource
already, so remove the dev_err call to avoid redundant
error message.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>