debugfs: fix encoding handling in dx_hash command

debugfs: fix encoding handling in dx_hash command

Fix the following bugs:

1. 'encoding' and 'hash_flags' are not initialized, causing a segfault.

2. 'hash_flags' incorrectly uses a __bitwise type.

3. The optstring doesn't contain "c" or "e", so the -c and -e options
   aren't recognized.

4. The code that handles the -e option always returns.

Fixes: ef733f1a97ec ("debugfs: support encoding when printing the file hash")
Reviewed-by: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>