vfio: Fix runaway interruptible timeout

vfio: Fix runaway interruptible timeout

Commit a6fb2660c9ae ("vfio: Add and use device request op for vfio
bus drivers") incorrectly makes use of an interruptible timeout.
When interrupted, the signal remains pending resulting in subsequent
timeouts occurring instantly.  This makes the loop spin at a much
higher rate than intended.

Instead of making this completely non-interruptible, we can change
this into a sort of interruptible-once behavior and use the "once"
to log debug information.  The driver API doesn't allow us to abort
and return an error code.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Fixes: a6fb2660c9ae
Cc: stable@vger.kernel.org # v4.0