Some clock driver do not have a clk_enable() call back, and we should not
treat this as fail in ehci probe like other modules, eg. clk_enabl_bulk()
do not return fail if ret value is '-ENOSYS'
Signed-off-by: Kever Yang <kever.yang@rock-chips.com> Reviewed-by: Patrice Chotard <patrice.chotard@st.com>