serial: xuartps: Fix the error handling logic in probe().

serial: xuartps: Fix the error handling logic in probe().

This patch reorder the error handling checks in probe()
to handle the failure conditions properly.

Signed-off-by: Nava kishore Manne <navam@xilinx.com>
Reviewed-by: Shubhrajyoti Datta <shubhraj@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>