usbmon: Use list_for_each_entry() helper

Convert list_for_each() to list_for_each_entry() so that the p/pos
list_head pointer and list_entry() call are no longer needed, which
can reduce a few lines of code. No functional changed.

Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Link: https://lore.kernel.org/r/20230830085658.527752-1-ruanjinjie@huawei.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>