debugfs: fix extent header in do_write for big-endian machines

Commit a17e9f30 set up the extent header for a new file.
Unfortunately it didn't correctly handle byte swapping; fix this so
the regression tests pass on PowerPC systems.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: Eric Sandeen <sandeen@redhat.com>
1 file changed