usb: dwc3: core: don't forget to free coherent memory

commit d9b4330a upstream.

commit 3921426b (usb: dwc3: core: move
event buffer allocation out of
dwc3_core_init()) introduced a memory leak
of the coherent memory we use as event
buffers on dwc3 driver.

If the driver is compiled as a dynamically
loadable module and use constantly loads
and unloads the driver, we will continue
to leak the coherent memory allocated during
->probe() because dwc3_free_event_buffers()
is never called during ->remove().

Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>