Correct comment in crypto/ec/curve448/ed448.h

Obvious Copy&Paste&not edit error.

CLA: trivial

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from #22573)

crypto/ec/curve448/ed448.h

@@ -21,7 +21,7 @@
 /* Number of bytes in an EdDSA private key. */
 # define EDDSA_448_PRIVATE_BYTES EDDSA_448_PUBLIC_BYTES
 
-/* Number of bytes in an EdDSA private key. */
+/* Number of bytes in an EdDSA signature. */
 # define EDDSA_448_SIGNATURE_BYTES (EDDSA_448_PUBLIC_BYTES + \
                                     EDDSA_448_PRIVATE_BYTES)