drivers: uio: Only allocate new private data when probing device tree node

The same condition should be used both when allocating and freeing the
driver private data.  When dev.of_node is non NULL, allocate a new
private data structure, otherwise use the values from the platform data.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Damian Hobson-Garcia <dhobsong@igel.co.jp>
Cc: "Hans J. Koch" <hjk@hansjkoch.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>