phy: stih41x-usb: Fixup stih41x_usb_phy_power_on failure path

If stih41x_usb_phy_power_on() fails, we need to call clk_disable_unprepare()
before return error. This is to ensure we have balanced clk_enable/disable
calls.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>