greybus: loopback: fix double error count

greybus: loopback: fix double error count

Make sure not count errors during asynchronous tests twice (first in
the timeout handler then again in the completion handler) to avoid
obviously broken error stats such as:

$ loopback_test -i 1000 -t transfer -p -o 200000 -c 64 -x -s 2000

1970-1-1 1:3:35
 test:                  transfer
 path:                  gb_loopback0
 size:                  2000
 iterations:            1000
 errors:                1998
 async:                 Enabled
 requests per-sec:      min=0, max=0, average=0.310556, jitter=0
 ap-throughput B/s:     min=0 max=4026 average=1254.647461 jitter=4026
 ap-latency usec:       min=12803 max=12803 average=12803.000000 jitter=0
 apbridge-latency usec: min=89 max=89 average=89.000000 jitter=0
 gpbridge-latency usec: min=294 max=294 average=294.000000 jitter=0

where we supposedly have more errors than iterations (operations
initiated).

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>