usb: phy-msm-usb: remove the unused alt core clock

The alt core clock is a substitute clock for the ulpi clock,
which comes from the phy. The phy does not provide ulpi clock
during reset and alt core clock is required at this time.

The USB controller on all active targets use asynchronous
reset and does not require alt core clock during phy reset.

Change-Id: Ic7b86c97a2ad59d90690a19bb49213ba7770d59b
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>