scpi/usbtmc: Implement Rigol DS1000 workaround on any firmware version.

scpi/usbtmc: Implement Rigol DS1000 workaround on any firmware version.

Firmware versions starting with 00.02.04 apparently cause the in and out
bulk endpoints to end up in a HALT state. This is likely related to the
larger transfer size quirk implemented in the Linux kernel for the Rigol
DS1000: this USBTMC implementation does not have that workaround.

Instead, if the firmware version is >= 00.02.04, both endpoints have the HALT
condition cleared on device close.

This fixes bug #354.