phy: phy-mtk-dp: Fix an error code in probe()

Negative -EINVAL was intended instead of positive EINVAL.

Fixes: 6a23afad ("phy: phy-mtk-dp: Add driver for DP phy")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Link: https://lore.kernel.org/r/3c699e00-2883-40d9-92c3-0da1dc38fdd4@moroto.mountain


Signed-off-by: Vinod Koul <vkoul@kernel.org>