fscrypt: don't special-case EOPNOTSUPP from fscrypt_get_encryption_info()

In fscrypt_setup_filename(), remove the unnecessary check for
fscrypt_get_encryption_info() returning EOPNOTSUPP.  There's no reason
to handle this error differently from any other.  I think there may have
been some confusion because the "notsupp" version of
fscrypt_get_encryption_info() returns EOPNOTSUPP -- but that's not
applicable from inside fs/crypto/.

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