drm/rockchip: fix integer type used for storing dp data rate

commit 2589c402 ("drm/rockchip: Avoid drm_dp_link helpers") changes
the type of variables used to store the display port data rate and
number of lanes to u8. However u8 is not sufficient to store the link
data rate of the display port.
This commit reverts the type of data rate to unsigned int.

Fixes: 2589c402 ("drm/rockchip: Avoid drm_dp_link helpers")
Signed-off-by: Tobias Schramm <t.schramm@manjaro.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20200109073129.378507-2-t.schramm@manjaro.org