clock: msm: Remove usb2_phy_sleep_clk from SSUSB

Now that the gcc_usb2{a,b}_phy_sleep_clk is mapped to
the HS PHY device, and the SSUSB driver is no longer
using this clock, remove the extraneous mappings.

Change-Id: I8d0554e50e409441a3baa67b5a629b74c0b74961
Signed-off-by: Jack Pham <jackp@codeaurora.org>