cipher:md: Check digest algo is supported when FIPS enabled.

* cipher/md.c (_gcry_md_hash_buffer): Check for FIPS for
hash_buffers method case.
(_gcry_md_hash_buffers_extract): Likewise.

For digest implementation with ->hash_buffers, there was no check.

• GnuPG-bug-id: T5665
• Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>