usb: phy: msm: Unregister VBUS and ID events notifiers

Right now even if driver failed to probe extcon framework will
still deliver its VBUS and ID events, which will lead to random
exception codes.

Fix this by removing VBUS and ID events notifiers when probe fail.

Fixes: 591fc116 ("usb: phy: msm: Use extcon framework for VBUS and ID detection")

Reported-by: Tim Bird <tim.bird@sonymobile.com>
Signed-off-by: Ivan T. Ivanov <ivan.ivanov@linaro.org>