i2c/dw: Switch from EPERM to EIO

The DW i2c driver chooses to return -EPERM following a PCI error in
driver configuration.  This seems an odd choice.  All of the other I2C
drivers return -EIO for general failures detected during driver
configuration.

Switch the DW driver from EPERM to EIO.

Change-Id: Ia4f96386620319736ae4c09212b0a05ea38169b1
Signed-off-by: Marcus Shawcroft <marcus.shawcroft@arm.com>