dwc3-msm: Enable cfg_ahb_clk before using AHB2PHY register

Commit a539b41f ("dwc3: Move usage of ahb2phy read/write wait
functionality to controller") has moved ahb2phy read/write wait
functionality with controller but in some cases AHB2PHY clock is
not explicitly turned ON which results into unclock register access.
Fix this issue by enabling cfg_ahb_clk before using AHB2PHY register.

Change-Id: I6db7880c39ec6b61d2f1f3caba160a06cc3bb42e
Signed-off-by: Mayank Rana <mrana@codeaurora.org>