debugfs: fix sprintf stack overflow

debugfs: fix sprintf stack overflow

The htree dump code overflows a char buffer if the directory has a long
filename because the buffer is not large enough to hold the characters that are
not part of the filename.  Make the buffer larger and use snprintf instead.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>