meson: libfido2 requires openssl

meson: libfido2 requires openssl

Fixes compile error with -Dopenssl=false.
```
In file included from ../../home/watanabe/git/systemd/src/shared/pkcs11-util.h:12,
                 from ../../home/watanabe/git/systemd/src/cryptenroll/cryptenroll.c:24:
../../home/watanabe/git/systemd/src/shared/openssl-util.h:56:21: error: conflicting types for ‘X509’; have ‘struct X509’
   56 | typedef struct X509 X509;
      |                     ^~~~
In file included from /usr/include/openssl/crypto.h:25,
                 from /usr/include/openssl/bio.h:20,
                 from /usr/include/openssl/asn1.h:16,
                 from /usr/include/openssl/ec.h:17,
                 from /usr/include/fido.h:10,
                 from ../../home/watanabe/git/systemd/src/shared/libfido2-util.h:18,
                 from ../../home/watanabe/git/systemd/src/cryptenroll/cryptenroll-fido2.h:7,
                 from ../../home/watanabe/git/systemd/src/cryptenroll/cryptenroll.c:6:
/usr/include/openssl/ossl_typ.h:123:24: note: previous declaration of ‘X509’ with type ‘X509’ {aka ‘struct x509_st’}
  123 | typedef struct x509_st X509;
      |                        ^~~~
```