generic/083: fix btrfs fs size for default mode

btrfs needs at least 256mb to create a FS with the defaults options.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/generic/083

@@ -71,7 +71,7 @@ workout()
 
 echo "*** test out-of-space handling for random write operations"
 
-filesize=`expr 100 \* 1024 \* 1024`
+filesize=`expr 256 \* 1024 \* 1024`
 agcount=6
 numprocs=15
 numops=1500