phy: samsung_usb2: Fixup samsung_usb2_phy_power_on/off paths

Ensure we have balanced clk_prepare_enable/clk_disable_unprepare calls if
.power_on or .power_off callbacks return error.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>