USB: dummy-hcd: Fix uninitialized array use in init()

USB: dummy-hcd: Fix uninitialized array use in init()

This error path

	err_add_pdata:
		for (i = 0; i < mod_data.num; i++)
			kfree(dum[i]);

can be triggered when not all dum's elements are initialized.

Fix this by initializing all dum's elements to NULL.

Acked-by: Alan Stern <stern@rowland.harvard.edu>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Bui Quang Minh <minhquangbui99@gmail.com>
Link: https://lore.kernel.org/r/1607063090-3426-1-git-send-email-minhquangbui99@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>