phy: uniphier-usb3ss: fix unintended writing zeros to PHY register

[ Upstream commit 898c7a9e ]

Similar to commit 4a90bbb4 ("phy: uniphier-pcie: Fix updating phy
parameters"), in function uniphier_u3ssphy_set_param(), unintentionally
write zeros to other fields when writing PHY registers.

Fixes: 5ab43d0f

 ("phy: socionext: add USB3 PHY driver for UniPhier SoC")
Signed-off-by: Ryuta NAKANISHI <nakanishi.ryuta@socionext.com>
Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Link: https://lore.kernel.org/r/1640150369-4134-1-git-send-email-hayashi.kunihiko@socionext.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>