f2fs: switch to using fscrypt_match_name()

Switch f2fs directory searches to use the fscrypt_match_name() helper
function.  There should be no functional change.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Acked-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>