Do not override an error from uiomove() with (non-)error result from bwrite().  VFS needs to know about EFAULT from uiomove() and does not care much that partially filled block writeback after EFAULT was successfull.  Early return without error causes short write to be reported to usermode.
Do not override an error from uiomove() with (non-)error result from
bwrite().  VFS needs to know about EFAULT from uiomove() and does not
care much that partially filled block writeback after EFAULT was
successfull.  Early return without error causes short write to be
reported to usermode.

Reported and tested by:	andreast
MFC after:	3 weeks

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase