phy: exynos5-usbdrd: fix setting LINKSYSTEM_FLADJ on exynos7870

The code here is trying to set the FLADJ field to 0x20, so it should
clear any previous value in that field before or'ing-in the new value.

Fixes: 588d5d20 ("phy: exynos5-usbdrd: add exynos7870 USBDRD support")
Signed-off-by: André Draszik <andre.draszik@linaro.org>
Link: https://lore.kernel.org/r/20250429-exynos5-phy-field-prep-v1-1-39eb279a3e0e@linaro.org


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