drivers/staging/fsl-mc: Fix DPIO error path issue

Remove unneeded call to dev_set_drvdata(dev, NULL) since the device
will be deallocated in any case.

Signed-off-by: Roy Pledge <roy.pledge@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>