ipmi: fix use after free in _ipmi_destroy_user()

The intf_free() function frees the "intf" pointer so we cannot
dereference it again on the next line.

Fixes: cbb79863 ("ipmi: Don't allow device module unload when in use")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Message-Id: <Y3M8xa1drZv4CToE@kili>
Cc: <stable@vger.kernel.org> # 5.5+
Signed-off-by: Corey Minyard <cminyard@mvista.com>