greybus: loopback: remove magic number in state-machine

Magic number 2 used instead of define GB_LOOPBACK_TYPE_PING, remove and and
use the define instead.
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/loopback.c

@@ -356,7 +356,7 @@ static int gb_loopback_fn(void *data)
 		gb->elapsed_nsecs = timeval_to_ns(&gb->te) -
 					timeval_to_ns(&gb->ts);
 		gb_loopback_freq_update(gb);
-		if (gb->type == 2)
+		if (gb->type == GB_LOOPBACK_TYPE_PING)
 			gb_loopback_bw_update(gb, error);
 		gb_loopback_latency_update(gb, &tlat);
 		if (gb->elapsed_nsecs >= NSEC_PER_SEC)