This fixes panic when listing sysctls on INVARIANTS-enabled kernel while
having wbwd loaded.
This panic was not fatal, at worst one additional space was printed.
Also sbuf_trim() makes some sense even if drain function is set. The drain
function is called only when buffer is to be expanded. So we could still trim
existing buffer before drain is called. In this case it worked just fine - the
trailing space was correctly trimmed.
Obtained from: WHEEL Systems
MFC after: 1 week
Winbond Super I/O chips.
With minor efforts it should be possible the extend the driver to support
further chips/revisions available from Winbond. In the simplest case
only new IDs need to be added, while different chipsets might require
their own function to enter extended function mode, etc.
Sponsored by: Sandvine Incorporated ULC (in 2011)
Reviewed by: emaste, brueffer
MFC after: 2 weeks
