Commit a4072543ccdddbd241d5962d9237b8b41fd006bf has changed the I/O here
from working on a local one-element I/O vector to just using the buffer
directly (using the bdrv_co_pread()/bdrv_co_pwrite() helper functions
introduced shortly before).
However, it only changed the bdrv_co_preadv() call to bdrv_co_pread() -
the subsequent bdrv_co_pwritev() call stayed this way, and so still
expects a QEMUIOVector pointer instead of a plain buffer. We must
change that to be a bdrv_co_pwrite() call.
Fixes: a4072543ccdddbd241d5962d ("block/parallels: use buffer-based io")
Signed-off-by: Hanna Reitz<hreitz@redhat.com>