USB: uss720: add debug endpoint-type check

Use the new endpoint helpers to lookup the interrupt-in endpoint,
and only print the corresponding debugging information in case it is
found.

Note that the descriptors are searched in reverse order to avoid any
regressions.

Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>