drm: xilinx: dp: Propagate the error code from devm_clk_get()

devm_clk_get() returns the error code other than -EPROBE_DEFER.
Return the error code from devm_clk_get() instead of always returning
-EPROBE_DFERE when devm_clk_get() fails.

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