mtd: onenand: omap2: Remove redundant dev_err call in omap2_onenand_probe()

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 <weiyongjun1@huawei.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>