phy: meson8b-usb2: fix missing clk_disable_unprepare() on error

Fix the missing clk_disable_unprepare() before return from
phy_meson8b_usb2_power_on() in the error handling case.

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>