usb: ehci-msm2: Fix controller autosuspend

When the EHCI controller is removed using platform_device_del(),
the PM disable_depth counter is decremented once by the driver
core. Thus the driver's remove callback additionally calling
pm_runtime_disable() is leading to an unbalanced counter since
pm_runtime_enable() call happens only once when platform_device_add()
calls the probe callback. Fix this by removing the extraneous
pm_runtime_disable().

Change-Id: Ie76256ac50ba65022814285bf57feca109f79d6b
Signed-off-by: Jack Pham <jackp@codeaurora.org>