drm: xilinx: dp: Fix the clock clean up code

Call clk_disable_unprepare() on error exit in xilinx_drm_dp_probe,
and change the order of calling clean up functions.

Signed-off-by: Hyun Kwon <hyun.kwon@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>