msm: clock-8084: Make set rate go through usb30 master clock

usb30_master_clk_src has two branch clocks: gcc_usb30_master_clk
and gcc_sys_noc_usb3_axi_clk. Since these branch clocks are
controlled by the same client driver and need to be turned on
and off at the same time, just set the sibling field of
gcc_usb30_master_clk to 0 to allow clk_set_rate on this clock
to simplify the clock control.

Change-Id: I00c79b04f3b5a17a62932d2d73755865d744962d
Signed-off-by: Tianyi Gou <tgou@codeaurora.org>