surface-scan: make bs 64k again

I reduced it for testing, put it back at 64k to speed it up.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/examples/surface-scan b/examples/surface-scan
index ae15846..dc3373a 100644
--- a/examples/surface-scan
+++ b/examples/surface-scan
@@ -2,7 +2,7 @@
 ; then verifies written data
 [global]
 thread=1
-bs=4k
+bs=64k
 direct=1
 ioengine=sync
 verify=meta