shared/005,7: fix making sure debugfs sets negative i_size

shared/005,7: fix making sure debugfs sets negative i_size

If the kernel bug has been fixed, stat command fails to get i_size
and reports "Structure needs cleaning".  So we use debugfs -R "stat"
instead of stat command to make sure debugfs sets negative i_size.
These cases have been broken by commit 0e13e40b247a1 ("shared/005,7:
make sure debugfs sets negative i_size").

Signed-off-by: Xiao Yang <yangx.jy@cn.fujitsu.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>