generic/487: reorder logdev detection after filesystem detection

If SCRATCH_LOGDEV variable is unset, the _require_logdev check fails
earlier than the following check that decides that this test should not
be run on 'btrfs'.

Signed-off-by: David Sterba <dsterba@suse.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/generic/487

@@ -36,7 +36,6 @@ _require_scratch_nocheck
 # This test uses "dm" without taking into account the data could be on
 # realtime subvolume, thus the test will fail with rtinherit=1
 _require_no_rtinherit
-_require_logdev
 
 sflag='-s'
 case $FSTYP in
@@ -47,6 +46,7 @@ case $FSTYP in
                 ;;
 esac
 
+_require_logdev
 _require_dm_target error
 
 rm -f $seqres.full