usb: phy: msm: Don't destroy_workqueue if wq not allocated

There is a possibility in existing code where destroy_workqueue
might be called even if wq is not allocated. Fix the error
handling path in probe function to handle this.

Change-Id: I447a7c284202281508eb74336fe8f3061d2e3daf
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>