usb: dwc3: Prevent use after free of dwc_ipc_log_ctx

The dbg_event function call in dwc3_msm_remove after the
child dwc3 device is removed is resulting in use after
free of dwc_ipc_log_ctx.
Even though the dwc_ipc_log_ctx is set to NULL in
dwc3_remove, the value is reset once the core platform
device is removed because the dwc3 is allocated using
devm_kzalloc. This call ensures that the memory is freed
up once the device driver is de-registered.
Fix this by calling the dbg_event before de-registering
the core driver.

Change-Id: Ib2cc3d233ea0fd4a1523cae23f57d3cb3753a53f
Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>