usb: gadget: Fix double free of device descriptor pointers

Upon driver unbind usb_free_all_descriptors() function frees all
speed descriptor pointers without setting them to NULL. In case
gadget speed changes (i.e from super speed plus to super speed)
after driver unbind only upto super speed descriptor pointers get
populated. Super speed plus desc still holds the stale (already
freed) pointer. Fix this issue by setting all descriptor pointers
to NULL after freeing them in usb_free_all_descriptors().

Fixes: f5c61225

 ("usb: gadget: Update function for SuperSpeedPlus")
cc: stable@vger.kernel.org
Reviewed-by: Peter Chen <peter.chen@kernel.org>
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>
Signed-off-by: Wesley Cheng <wcheng@codeaurora.org>
Link: https://lore.kernel.org/r/1619034452-17334-1-git-send-email-wcheng@codeaurora.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>