fpga: xilinx-pr-decoupler: Simplify code by using dev_err_probe()

Use already prepared dev_err_probe() introduced by commit a787e540
("driver core: add device probe log helper").
It simplifies EPROBE_DEFER handling.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Moritz Fischer <mdf@kernel.org>