fscrypt: remove unnecessary check for non-logon key type

We're passing 'key_type_logon' to request_key(), so the found key is
guaranteed to be of type "logon".  Thus, there is no reason to check
later that the key is really a "logon" key.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>