PCI: imx6: Remove redundant dev_err() in imx6_pcie_probe()

There is an 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: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>