msm: clock-8226: Add sleep clock for USB 2.0 PHY

USB 2.0 PHY is provided sleep clock. Add USB otg
device name and rename sleep_a_clk to sleep_clk to
allow USB driver to get sleep clock handle and vote
for the same.

Remove ref_clk entry from clock table as it is not
available with USB PHY on this platform. Hence it is
unused entry for this platform.

CRs-Fixed: 518359
Change-Id: I1c6e2eb2a281da9dc2bb420673d06abefbff7507
Signed-off-by: Mayank Rana <mrana@codeaurora.org>